Method of manufacturing semiconductor device, acid etching resistance material and copolymer

ABSTRACT

Disclosed is an acid etching resistance material comprising a compound having a repeating unit represented by the following general formula (1): 
     
       
         
         
             
             
         
       
         
         
           
             (in the general formula (1), R 1  is a hydrogen atom or methyl group; R 3  is a cyclic group selected from an alicyclic group and an aromatic group; R 4  is a polar group; R 2  is a group represented by the following general formula (2); and j is 0 or 1): 
           
         
       
    
     
       
         
         
             
             
         
       
         
         
           
             (in the general formula (2), R 5  is a hydrogen atom or methyl group).

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation application of U.S. patentapplication Ser. No. 11/679,660, filed Feb. 27, 2007; which in turn,claims priority to U.S. patent aplication Ser. No. 11/056,094, filedFeb. 14, 2005, which in turn, claims the benefit of priority from priorJapanese Patent Applications No. 2004-108108, filed Mar. 31, 2004; andNo. 2004-173864, filed Jun. 11, 2004. This application claims priorityto the following applications: U.S. patent application Ser. No.11/679,660, U.S. patent application Ser. No. 11/056,094, Japanese PatentApplication No. 2004-108108, and Japanese Patent Application No.2004-173864; the entire contents of each of these applications areincorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to a method of manufacturing a semiconductordevice, to an acid etching resistance material, and to a copolymer.

2. Description of the Related Art

A compound semiconductor to be employed for constituting a lightemitting element is generally very high in refractive index, so thatmost light emitting elements suffer loss of light due to the reflectionof light at the surface or interface thereof. Therefore, it has beendifficult to externally retrieve the light that has been generatedinside the light emitting elements at a high efficiency. In the case ofcompounds such as gallium phosphide, the refractive index thereof is ashigh as 3.5 or so, so that because of the total reflection thereof, only19% of incident light can be taken out. To cope with this problem, it isusual conducted to form, as an antireflection layer, a monolayer filmhaving a refractive index of about 1.5 on the surface of a lightemitting element. However, since the difference in refractive indexbetween the light-emitting surface and the monolayer film is relativelylarge, the light emitting element constructed as described above isstill insufficient to overcome the aforementioned problem.

As a measure for enhancing the light extracting efficiency, there isknown a method wherein the surface of light emitting element isroughened to increase the surface area of the light emitting element,thus enhancing the external quantum yield. The roughening of the surfaceof light emitting element can be generally performed by surfacetreatment using an etching solution comprising hydrochloric acid,sulfuric acid, hydrofluoric acid, hydrogen peroxide or a mixturethereof. In this case, since a specific crystal face of compoundsemiconductor corrades when the compound semiconductor is subjected towet etching, a pattern of triangular pyramid-like configuration having asize of the order of μm would be formed depending on crystal face. As aresult, the surface area of the light emitting element is increased,resulting in an increase of the light extracting efficiency and hencethe enhancement of luminance.

The surface-roughening treatment by this chemical etching is called a“frosting treatment” and can be executed by a very simple technique,i.e., by simply dipping a compound semiconductor in an etching solution.More specifically, this frosting treatment is performed with the entiresurfaces of the compound semiconductor substrate, excluding the surfacewhere the roughening is taken place, being covered with a protectingfilm so as to prevent the electrodes, for instance, from being contactedwith etching solution. The protecting film to be employed herein isrequired to be such that it can be easily removed after finishing thefrosting treatment and at the same time, it is resistive to the etchingsolution. However, no one has succeeded as yet to obtain a materialhaving such characteristics as described above.

Meanwhile, there is known an optical pattern etching method which is afine fabrication technique for etching a substrate so as to form anoptical pattern on the surface thereof, this optical pattern etchingmethod comprising a step of coating a photosensitive hydrofluoric acidetching resist material on the substrate, a step of exposure, a step ofdevelopment, and a step of etching. This optical pattern etching methodis one of elemental techniques to be employed in the manufacture of alarge-scale integrated circuit (LSI) substrate and is also applied tothe manufacture of a micro-electromechanical system (MEMS) of opticalscanning apparatus, and the manufacture of semiconductor devices such asa light-emitting diode (LED) in recent years.

In particular, the etching step using hydrofluoric acid in theaforementioned optical pattern etching method is expected to beapplicable to the etching of a sacrificial layer of an optical scanningapparatus having a movable element structure and provided with anoptical waveguide which is low in hydrofluoric acid resistance, or tothe frosting treatment of LED for enhancing the light extractingefficiency through the roughening of the surface of light emittingelement made from a compound semiconductor. In this case, in order toshorten the running time of the manufacturing method, it is desirable toemploy concentrated hydrofluoric acid (for example 49%) in the etchingstep.

However, the manufacture of an LSI substrate is mainly performed byetching using dilute hydrofluoric acid due to the facts that theconventional photo-sensitive etching material that has been developedfor the manufacture of LSI substrate is poor in resistance tohydrofluoric acid and that a photosensitive hydrofluoric acid etchingresist material to which concentrated hydrofluoric acid can beapplicable is not yet available. Accordingly, if concentratedhydrofluoric acid etching is to be performed, the portions which aremade of a material poor in hydrofluoric acid resistance are required tobe formed after finishing the step of hydrofluoric acid etching, thusraising problems that the manufacturing process is complicated and themanufacturing period is prolonged.

BRIEF SUMMARY OF THE INVENTION

According to one aspect of the present invention, there is provided amethod of manufacturing a semiconductor device comprising asemiconductor substrate having a first electrode provided above the rearsurface thereof and roughened side surfaces; a light emitting layerformed above the semiconductor substrate; and a second electrodeprovided above the light emitting layer or above the rear surface; saidmethod comprising:

forming a protective film above an entire surfaces of the semiconductorsubstrate including the first electrode, the light emitting layer andthe second electrode, excluding the side surfaces, the protective filmcomprising an acid etching resistance material having a repeating unitrepresented by the following general formula (1):

(in the general formula (1), R¹ is a hydrogen atom or methyl group; R³is a cyclic group selected from an alicyclic group and an aromaticgroup; R⁴ is a polar group; R² is a group represented by the followinggeneral formula (2); and j is 0 or 1:

(in the general formula (2), R⁵ is a hydrogen atom or methyl group);

treating the semiconductor substrate having the protective film formedthereof with an acidic etching solution; and

removing the protective film with an alkaline solution.

According to another aspect of the present invention, there is providedan acid etching resistance material comprising a compound having arepeating unit represented by the following general formula (1):

(in the general formula (1), R¹ is a hydrogen atom or methyl group; R³is a cyclic group selected from an alicyclic group and an aromaticgroup; R⁴ is a polar group; R² is a group represented by the followinggeneral formula (2); and j is 0 or 1):

(in the general formula (2), R⁵ is a hydrogen atom or methyl group).

According to another aspect of the present invention, there is provideda copolymer comprising:

40 to 70 mol % of 3-hydroxy-1-methacryloyloxy-adamantane represented bythe following chemical formula (A2); and

the balance of 2-acryloyloxypropyl phthalate represented by thefollowing chemical formula (A4):

According to another aspect of the present invention, there is providedan acid etching resistance material comprising:

a resin having at least two kinds of repeating units represented by thefollowing general formula (PS1); and

a photo acid generator which is capable of generating an acid as it isirradiated with light:

(in the general formula (PS1), R¹¹ and R¹³ are individually a hydrogenatom or methyl group; R¹² is selected from the group consisting ofadamantane, tricyclodecane, norbornane, isobornane, cyclohexane andcyclooctane, each having one or two hydroxyl groups; R¹⁴ is selectedfrom the group consisting of adamantane, tricyclodecane, norbornane,isobornane, cyclohexane and cyclooctane, each having one ketone groups;and m and n represent individually a natural number).

According to another aspect of the present invention, there is provideda method of manufacturing a semiconductor device comprising:

forming a layer of a photosensitive etching resistance material on asubstrate made of semiconductor or quartz glass, the photosensitiveetching resistance material comprising an acid etching resistancematerial composed of a resin having at least two kinds of repeatingunits represented by the following general formula (PS1); and a photoacid generator which is capable of generating an acid as it isirradiated with light:

(in the general formula (PS1), R¹¹ and R¹³ are individually a hydrogenatom or methyl group; R¹² is selected from the group consisting ofadamantane, tricyclodecane, norbornane, isobornane, cyclohexane andcyclooctane, each having one or two hydroxyl groups; R¹⁴ is selectedfrom the group consisting of adamantane, tricyclodecane, norbornane,isobornane, cyclohexane and cyclooctane, each having one ketone groups;and m and n represent individually a natural number):

subjecting the substrate to patterning exposure;

heating the substrate;

subjecting the substrate to a developing treatment using an alkalinedeveloping solution; and

subjecting the substrate to a fluoric acid etching treatment using asolution containing fluoric acid at a concentration ranging from 30% to50%.

According to another aspect of the present invention, there is provideda method of manufacturing a semiconductor device comprising:

forming a sacrificial layer composed of quartz glass on a semiconductorsubstrate;

forming an element structure composed of semiconductor on thesacrificial layer;

forming a region composed of a material which is poor in hydrofluoricacid resistance on the semiconductor substrate;

covering the region composed of a material which is poor in hydrofluoricacid resistance with a photosensitive etching resistance materialcomprising an acid etching resistance material composed of a resinhaving at least two kinds of repeating units represented by thefollowing general formula (PS1); and a photo acid generator which iscapable of generating an acid as it is irradiated with light:

(in the general formula (PS1), R¹¹ and R¹³ are individually a hydrogenatom or methyl group; R¹² is selected from the group consisting ofadamantane, tricyclodecane, norbornane, isobornane, cyclohexane andcyclooctane, each having one or two hydroxyl groups; R¹⁴ is selectedfrom the group consisting of adamantane, tricyclodecane, norbornane,isobornane, cyclohexane and cyclooctane, each having one ketone groups;and m and n represent individually a natural number); and

removing the sacrificial layer by applying a hydrofluoric acid solutionto the semiconductor substrate.

According to another aspect of the present invention, there is provideda method of manufacturing a semiconductor device comprising:

forming a region of a material which is excellent in hydrofluoric acidresistance on a semiconductor substrate;

forming a region of a material which is poor in hydrofluoric acidresistance over the region which is composed of a material which isexcellent in hydrofluoric acid resistance;

covering the region which is poor in hydrofluoric acid resistance with aphotosensitive etching resistance material comprising an acid etchingresistance material composed of a resin having at least two kinds ofrepeating units represented by the following general formula (PS1); anda photo acid generator which is capable of generating an acid as it isirradiated with light:

(in the general formula (PS1), R¹¹ and R¹³ are individually a hydrogenatom or methyl group; R¹² is selected from the group consisting ofadamantane, tricyclodecane, norbornane, isobornane, cyclohexane andcyclooctane, each having one or two hydroxyl groups; R¹⁴ is selectedfrom the group consisting of adamantane, tricyclodecane, norbornane,isobornane, cyclohexane and cyclooctane, each having one ketone groups;and m and n represent individually a natural number); and

subjecting the region which is composed of a material which is excellentin hydrofluoric acid resistance to an etching treatment using a solutionof hydrofluoric acid.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING

FIG. 1 is a diagram schematically illustrating the design manual formolecular design according to one embodiment of the present invention;

FIG. 2 is a diagram schematically illustrating the relationship betweenthe composition of copolymer and a spec required for a protective filmfor frost treatment;

FIG. 3 is a cross-sectional view of a light emitting element which wasmanufactured by the method according to one embodiment of the presentinvention;

FIG. 4 is an NMR chart of an acid etching resistance material accordingto one embodiment of the present invention;

FIG. 5 is a cross-sectional view illustrating the step of themanufacturing method of a semiconductor device according to oneembodiment of the present invention;

FIG. 6 is a cross-sectional view illustrating a step to be executedfollowing the step shown in FIG. 5;

FIG. 7 is a cross-sectional view illustrating a step to be executedfollowing the step shown in FIG. 6;

FIG. 8 is a cross-sectional view illustrating a step to be executedfollowing the step shown in FIG. 7;

FIG. 9 is a cross-sectional view illustrating a step to be executedfollowing the step shown in FIG. 8;

FIG. 10 is a cross-sectional view illustrating a step to be executedfollowing the step shown in FIG. 9;

FIG. 11 is a cross-sectional view illustrating a step to be executedfollowing the step shown in FIG. 10;

FIG. 12 is a cross-sectional view illustrating a step to be executedfollowing the step shown in FIG. 11;

FIG. 13 is a flowchart illustrating a method of synthesizing a resinaccording to another embodiment of the present invention;

FIGS. 14A and 14B show respectively a top view illustrating an opticalscanning apparatus representing another embodiment of the presentinvention;

FIG. 15 shows a partial sectional view schematically illustrating anoptical scanning apparatus representing another embodiment of thepresent invention;

FIG. 16 shows a cross-sectional view schematically illustrating an LEDrepresenting another embodiment of the present invention; and

FIGS. 17A to 17I show respectively a cross-sectional view schematicallyillustrating a method of manufacturing an optical scanning apparatusemployed in a test (E).

DETAILED DESCRIPTION OF THE INVENTION

Specific embodiments of the present invention will be explained asfollows.

Embodiment 1

The method of manufacturing a semiconductor device according to oneembodiment of the present invention is applicable especially to themanufacture of a light emitting element. In the process of thismanufacturing method of a light emitting element, a compoundsemiconductor substrate is treated with a mixed solution consisting ofhydrochloric acid and hydrogen peroxide (hydrofluoric acid/hydrogenperoxide), and then surface-treated with concentrated hydrofluoric acid,thereby roughening the surface of the compound semiconductor substrate.By the term “concentrated hydrofluoric acid”, it is intended to indicatea solution containing hydrofluoric acid at a concentration of 25% ormore. It is desirable, in order to enhance the emission efficiency oflight emitting element, to employ a solution of hydrofluoric acidcontaining hydrofluoric acid at a very high concentration of 40% ormore. Since this concentrated hydrofluoric acid is employed as anetching solution, a protective film to be employed in this case isrequired to be resistive not only to hydrochloric acid/hydrogen peroxidebut also to concentrated hydrofluoric acid. Moreover, the protectivefilm is required to be alkali-soluble so as to enable the protectivefilm to be easily removed by using an alkaline solution subsequent tothe surface-roughening treatment of semiconductors. As for the alkalinesolution, it is possible to employ, for example, an alkaline developingsolution for semiconductors (for example, a 2.38% aqueous solution oftetramethyl ammonium hydroxide (TMAH)). It is also possible to employany kind of alkaline solution as long as it is adapted to be employed inthe treatment of semiconductors.

In order to make the resin constituting the protective filmalkali-soluble, the resin is required to be hydrophilic. There is a verynarrow choice in finding a resin which is not only hydrophilic but alsoexcellent in acid resistance. In particular, it is very difficult tofind a material which is resistive to hydrofluoric acid and at the sametime, excellent in alkali-solubility.

The present inventors have made extensive studies with a view to obtaina resin which can be employed as a protective film satisfying all of theaforementioned conditions.

Incidentally, as for specific examples of the polymeric materials whichare resistive to both of hydrofluoric acid and hydrochloric acid, theyinclude butyl rubber, fluororubber, polyethylene, polypropylene, acrylicresin, Teflon (registered trademark) (PTFE, ETFE), and phenolic resin.As for the fluororubber and Teflon, since there is no solvent availablefor them, they cannot be employed. As for polyethylene andpolypropylene, although they are soluble in a chlorine-based solvent,they are not applicable to alkaline development since they are notprovided with hydrophilic moiety at all. Further, because of badinfluences to environments, most of hydrochloric acid-based solventscannot be employed at present. Due to the aforementioned problems,resins which are expected to be useful are confined to acrylic resin andphenolic resin.

Phenolic resin is a resin which is now employed as an ordinaryphotoresist. For example, novolac can be employed as a photoresist forg-line or i-line. Polyhydroxystyrene (PHS) is employed as a photoresistfor KrF excimer laser. Therefore, the ordinary photoresist (OFPR-800:Tokyo Ohka Co., Ltd., a mixture comprising novolac and naphthoquinonediazide (photosensitive agent)) and polymethylmethacrylate (PMMA) whichis a representative acrylic resin were compared with each other at firstwith regard to the hydrofluoric acid resistance thereof.

Each of these resins was dissolved in propyleneglycol monomethyl etheracetate (PGMEA) to form a solution, which was then coated on a galliumphosphide substrate by spin coating method to form a resin layer. Thisresin layer was then immersed in concentrated fluoric acid for 20minutes to perform the etching of the substrate. As a result, theOFPR-800 was removed from the substrate in about 5 minutes, and theresultant exposed surface of the substrate was turned cloudy due to theetching. On the other hand, to the PHS with 23% of hydroxyl groupthereof being protected with t-butoxycarbonyl, 0.5% by weight oftriphenylsulfonium trifluoromethane sulfonate was added to prepare apolyhydroxystyrene-based resist, which was then evaluated in the samemanner as described above. As a result, it was found that when a resinlayer comprising this resist was immersed in concentrated fluoric acid,the resin layer was peeled away from the substrate in about 5 minutesand at the same time, the resin was decomposed by the effect of thehydrofluoric acid. In the case of the PMMA however, even though theresin layer was peeled away from the substrate, the resin layer wasfloated in the hydrofluoric acid and to remain as it was without beingdecomposed for several tens minutes. It was confirmed that even in thecase of PMMA having one of the simplest structures of acryl, thehydrofluoric acid resistance thereof was higher than that of theconventional resist.

As a result, it was determined that the main chain of a hydrofluoricacid resistance resin should be constituted by an acrylic backbone.Moreover, it is required that this acrylic main chain is protected so asnot to be decomposed by the attack from hydrofluoric acid. It was foundthat this requirement could be met by introducing an alicyclic compound(alicyclic group) excellent in chemical stability or an aromatic ringexcellent in chemical stability into a side chain of the resin.

As for specific examples of alicyclic hydrocarbon, they include, forexample, cyclopentane, cyclohexane, cyclooctane, norbornane, isobornane,adamantane and tricyclodecane. It is also possible to employ cyclobutanering, cyclopentane ring, cyclohexane ring, cycloheptane ring,cyclooctane ring, each of them comprising a bridging hydrocarbon,norbornane ring, adamantane ring, bornane ring, terpene ring such asmenthane ring, etc. Among them, alicyclic hydrocarbon having asix-membered ring is more preferable due to the excellent chemicalstability thereof, specific examples of such alicyclic hydrocarbonincluding adamantane, norbornane, isobornane, tricyclodecane andcyclohexane. An alicyclic compound having one or more crosslinkingstructures is known to have a hard structure which is close to that ofdiamond and also known to be very excellent in chemical stability.Therefore, the employment of adamantane, norbornane, isobornane andtricyclodecane is especially preferable. Further, as for specificexamples of the aromatic ring, they include benzene ring and naphthalenering. Since benzene ring is less bulky and is capable of suppressing thecreation of spaces inside a high-molecular chain to make it possible tominimize free volume as compared with naphthalene ring, the employmentof benzene ring is more preferable.

Although it is possible through the employment of alicyclic group andaromatic ring to protect the main chain of acrylic backbone from beingattacked by hydrofluoric acid, these alicyclic group and aromatic ringare strong in hydrophobicity. Therefore, if the resin layer comprisingany of these alicyclic group and aromatic ring is to be removed from thesubstrate, it is required to employ an organic solvent. In order to makethe resin layer soluble in an ordinary resist developing solution whileretaining the alkali-solubility of the resin layer, a polar group isfurther attached to a terminal of the side chain of polymer. As for thepolar group useful in this case, it is possible to employ carboxylgroup, hydroxyl group or ketone.

FIG. 1 illustrates the schematic design for molecular design, whichmeets the aforementioned conditions. As shown in FIG. 1, the main chainfor retaining the entire structure of polymer is composed of an acrylicbackbone, to which a cyclic group such as alicyclic group or aromaticring is attached as a side chain, thereby enhancing the hydrofluoricacid resistance. Additionally, a polar group is linked to the cyclicgroup for securing the adherence of polymer to a substrate.

The acrylic resin having such a side chain can be synthesized accordingto the following flow chart for instance.

-   -   |←Charging of monomers;    -   |←Charging of AIBN, 1 mol %/monomer;    -   |←Charging of THF, about three times based on the weight of the        monomer;    -   |←Replacement of atmosphere by a nitrogen atmosphere;    -   |    -   |→Reaction: performed for 40 hours at 60° C. in a nitrogen        atmosphere;    -   |    -   |←2 mL of methanol is added to the reaction solution to        eliminated radicals;    -   |←While agitating the reaction solution in Erlenmeyer flask,        hexane (2 to 3 times as much as THF) was added drop-wise to the        reaction solution to form reprecipitate;    -   | The agitation is continued to turn the initially gel-like        material into powder;    -   |    -   |→Solvent is removed by filtration;    -   |←Vacuum drying (60° C. for 2-3 days);    -   |→Molecular weight is measured by GPC: when there is residual        monomer, it is dissolved in THF to form reprecipitate;    -   |    -   |→Yield: 80-90%.

First of all, 0.01 mol of azobisisobutyronitrile (AIBN) was added as apolymerization initiator to a monomer to obtain a mixture, which wasthen diluted with tetrahydrofuran (THF) at a weight ratio of 2 to 3times as much as the monomer. The resultant mixture was then agitated ina nitrogen atmosphere so as to allow a reaction to take place for 40hours at a temperature of 60° C. To this resultant solution was addeddrop-wise n-hexane to allow a polymer component to precipitate to refinethe polymer. Although a radical polymerization method is illustrated inthe above embodiment, it is also possible to synthesize the same kind ofacrylic resin by other methods such as cationic polymerization methodand anionic polymerization method.

Cyclic groups such as the aforementioned alicyclic group and aromaticring are highly bulky and are also expected to exhibit excellentresistance to hydrofluoric acid. Therefore, a cyclic group wasintroduced into the side chain of polymer in the synthesis of theacrylic resin. Since a lot of time is required if a multifunctionalresin is to be synthesized from the beginning, resins were synthesizedonly for the purpose of examining the function of hydrofluoric acidresistance, the resins including poly(t-butylmethacrylate),poly(adamantylmethacrylate), poly(isobornylmethacrylate),poly(cyclohexane methacrylate) and poly(phenoxyethylacrylate). Sincethese resins are poor in solubility to a solvent, it is difficult toobtain a flat film. Further, since these resins are highly hydrophobic,they cannot be dissolved in an alkaline solution. Additionally, each ofthese resins are insufficient in adhesion to a substrate, however, theseresins are sufficient to evaluate the resistance to hydrofluoric.

Then, each of the resins was dissolved in cyclohexane and the resultantsolution was spin-coated on gallium phosphide substrate to form a film.Due to poor solubility of the resins, it was impossible to form auniform film. However, it was possible to form samples of resin layershaving a film thickness of about several micrometers. When these sampleswere immersed in a solution of concentrated hydrofluoric acid, bubbleswere generated from the surfaces of these samples within about 5 secondsand then to peel away from the substrate as a fine strip of resin, thusthe resin layer floated near the surface of the solution. Due to thefact that the pieces of resin thus kept floating existed as they werewithout being decomposed in the solution of concentrated hydrofluoricacid even after one hour, it was confirmed that these resins could notbe decomposed by the effect of hydrofluoric acid.

The resins synthesized herein were peeled off due to the fact that theywere in defect of a moiety which was capable of adhering to thesubstrate. However, with regard to the hydrofluoric acid resistancewhich was essential to these resins, there was no problem. As a resultof above experiments, it has been found that even with a thin film madeof acrylic resin, it is possible to make it sufficiently resistive toconcentrated hydrofluoric acid if a structure which is capable ofprotecting the main chain is introduced into the side chain.

For the purpose of enhancing the adhesion of resin layer to a substrate,carboxyl group was introduced into an alicyclic compound suspended asthe side chain. By introducing an acidic carboxyl group into the sidechain, the resin layer was turned alkali-soluble, thereby making itpossible to dissolve and remove the resin layer by using an alkalinedeveloping solution. The polymers thus synthesized can be classifiedinto four kinds, i.e., two kinds consisting of methacrylate whereα-position thereof is constituted by methyl group and acrylate whereα-position thereof is constituted by hydrogen atom; and two kindsconsisting of a polymer where the side chain thereof is constituted byalicyclic group and a polymer where the side chain thereof isconstituted by aromatic ring. The chemical structures of these fourkinds of polymers are illustrated below.

As for two samples of methacrylate-based polymers, [A]2-methacryloyloxyethyl phthalate (Acryester PA) and [B]2-methacryloyloxyethyl hexahydrophthalate (Acryester HH) were obtainedfrom Mitsubishi Rayon Co., Ltd. As for two samples of acrylate-basedpolymers, [C] 2-acryloyloxypropyl phthalate (Viscoat 2100) and [D]2-acryloyloxypropyl hexahydrophthalate (Viscoat 2150) were obtained fromOhsaka Organic Chemical Industry Ltd. These monomers were polymerizedaccording to the method illustrated in the aforementioned flowchart toobtain polymers.

Each of these polymers was investigated with respect to the solventsolubility, hydrofluoric acid resistance and alkali-solubility thereof.Each of the performances was evaluated according to the followingcriterions, the results obtained being summarized in the following Table1.

(Solvent Solubility)

A: Solubility to the organic solvent was poor

B: More or less soluble to the organic solvent

C: Little problem with regard to solubility

D: No problem at all with regard to solubility

(Hydrofluoric Acid Resistance)

A: Impossible to measure

B: Relatively poor in hydrofluoric acid resistance

C: Fairly good in hydrofluoric acid resistance

D: Hydrofluoric acid resistance is more or less recognizable

(Alkali-Solubility)

A: None

B: Although soluble but incompletely

C: Soluble

D: Very good in solubility

TABLE 1 Solvent Hydrofluoric Alkali- solubility acid resistancesolubility ViscoatViscoat A B C 2100 VViscoat A C A 2150 Acryester PA D— — Acryester HH B D D~C

Viscoat 2100 and Viscoat 2150 are almost the same in molecular structureand differ from each other only in the respect that the cyclic groupthat has been introduced into the side chain is whether aromatic ring(benzene ring) or an alicyclic group (cyclohexane ring). In the casewhere the chemical structure is similar to each other as describedabove, when these two kinds of monomers are mixed with each other so asto copolymerize them, the characteristics of the copolymer arefrequently commensurate with the ratio of composition. In this case,when Viscoat 2100 which is relatively excellent in hydrofluoric acidresistance is copolymerized together with Viscoat 2150 which is veryexcellent in alkali-solubility, it is possible to obtain a resinprovided with all of the aforementioned characteristics.

Viscoat 2100 and Viscoat 2150 were mixed together at various ratios toobtain five polymer samples. The Table 2, below illustrates mixing ratio(mol %) of the Viscoat 2100.

TABLE 2 Sample No. 1 2 3 4 5 Ratio of Viscoat 2100 (mol %) 100 75 50 250

Each of these polymers was dissolved in PGMEA to prepare a solutioncontaining the polymer at a concentration of 30% by weight. Theresultant solutions were respectively coated on gallium phosphidesubstrate by spin coating method at a rotational speed of 100 rpm toform a resin layer having a thickness of about 3 μm. When the substrateseach having the resin layer formed thereon was immersed in concentratedhydrofluoric acid for 20 minutes, the resin films of the samples Nos. 1,2 and 3 were turned cloudy. In order to ensure the hydrofluoric acidresistance of the resin layer, the content of Viscoat 2100 shoulddesirably be not less than 50 mol %. 20 minutes later, these sampleswere picked up from the hydrofluoric acid and washed with pure water anddried. As a result, it was confirmed that the thickness of the resinlayer was not changed at all in every samples, thus indicating that theresin itself could not be decomposed by the concentrated hydrofluoricacid. When the removal of the resin layer through the dissolutionthereof was tried by using an alkaline developing solution (AD-10; TamaKagaku Co., Ltd.), the resin layer in samples 4 and 5 was dissolve inthe order of several seconds. However, it took several minutes indissolving the resin layer as the content of Viscoat 2100 was increased.

When these samples were immersed in the alkaline developing solutionimmediately after these samples were immersed in the concentratedhydrofluoric acid, the resin layer was completely dissolved within oneminute in all of the samples. However, when these samples were oncedried after the immersion thereof in the concentrated hydrofluoric acid,it took about one hour in dissolving the resin layer especially when thecontent of Viscoat 2100 was increased as in the case where thedissolution of resin layer was tried immediately after the coatingthereof. The reason for this may be attributed to the fact that thealkaline developing solution penetrated into the resin layer as theresin layer was swelled in the concentrated hydrofluoric acid, thusenabling the resin layer to be dissolved also from the interior thereof.Especially when the content of Viscoat 2100 was increased to 50 mol % ormore, there was not visually recognized any corrosion of substrate inthe gallium phosphide substrates from which the resin layer dissolved inthe alkaline developing solution. Therefore, it is desirable that thecontent of Viscoat 2100 in the resin is increased to 50 mol % or more inorder to secure a sufficient hydrofluoric acid resistance. When thecontent of Viscoat 2100 is 100 mol % (Sample 1) however, the viscosityof the solution would become too high so that the film coated on thesubstrate is more likely to shrink. Therefore, it is considered that anoptimum mixing ratio of Viscoat 2100 would be about 75 mol %.

Then, acrylic resins where adamantane ring was introduced into the sidechain of polymer were synthesized according to the aforementionedflowchart. The chemical structures of the resins thus obtained are asshown below.

Each of the resins and the monomers thereof are summarized below.

-   -   (PA1): 5-methacryloyloxy-adamanthan-2-one (A1)    -   (PA2): 3-hydroxy-1-methacryloyloxy-adamantane (A2)    -   (PA3): 3-carboxy-1-methacryloyloxy-adamantane (A3)    -   (PA4): 2-acryloyloxypropyl phthalate (Viscoat 2100, A4)

Each of these resins was investigated with respect to the solventsolubility, hydrochloric acid (+hydrogen peroxide) resistance,hydrofluoric acid resistance, neutralizing solution resistance andalkali-solubility thereof. The results obtained are summarized in thefollowing Table 3. Incidentally, the solvent solubility, hydrofluoricacid resistance and alkali-solubility thereof were evaluated accordingto the same criterions as described above. The hydrochloric acid(+hydrogen peroxide) resistance was evaluated according to the followingcriterion. With respect to characteristics of Viscoat 2100, theevaluation thereof was performed in the same manner as described above.

(Hydrochloric acid (+hydrogen peroxide) resistance; resistance)

A: Resistive to both of these materials

B: Not resistive to hydrofluoric acid/hydrogen peroxide, but resistiveto hydrofluoric acid

C: Resistive to hydrofluoric acid/hydrogen peroxide, and also weaklyresistive to hydrofluoric acid

D: Not resistive to both of these materials

TABLE 3 (HPA1) (HPA2) (HPA3) (HPA4) Solvent solubility B C D Bhydrofluoric acid D B D B resist. (+hydrogen peroxide) Hydrofluoric acidA B D C resist. Neutralizing liquid resist. Alkali-solubility D D A A

The reason for the incapability of (PA1) of resisting hydrochloric acidis assumed to be attributed to the fact that ketone (=O) was decomposeddue to effect of the acid. However, when content of the monomer (A1) was50 mol % or more, the resultant resin exhibited excellent resistanceagainst both of hydrofluoric acid and neutralizing liquid.

In the case of (PA2) where hydroxyl group was bonded to a terminal ofadamantane, although it was more or less resistive to hydrofluoric acid,it was incapable of substantially resisting hydrofluoric acid as it wasemployed singly. (PA2) was sufficiently capable of resistinghydrochloric acid, and it was possible, through a combination thereofwith other kinds of polymers, to make it to exhibit solubility to asolvent.

In the case of (PA3) which was carboxylic acid-based, although itexhibited excellent alkali-solubility, the polarity thereof was too highso that it was not dissolved in an ordinary resist solvent adapted to beemployed in a spin coating. Further, due to high crystallinity of (PA3),the thin film thereof formed by spin coating subsequently crystallized,thus the thin film fractured.

In the case of (PA4), although the neutralizing liquid penetratedtherein, it was possible to dissolve it in the developing solution byincreasing the mixing ratio of the monomer (A4) up to 30 mol % or more.

Therefore, it was determined to employ the carboxylic acid-based monomerwhich was excellent in adhesion to the substrate and inalkali-solubility in combination with the monomer (A4) which was foundexcellent in adhesion to the substrate as a result of studies inExample 1. The copolymer thus obtained was a random polymer where thesemonomers were incorporated in a chain at random at a certain ratio.

In the foregoing examples, acrylic resin containing adamantane wasexplained. However, since an alicyclic compound having one or morecross-linking structures is very excellent in chemical stability, it ispossible to obtain the same results as described above even if any ofnorbornane, isobornane and tricyclodecane is employed.

The kinds of monomers included in each of the copolymers are summarizedin the Table 4, below.

TABLE 4 Copolymers C1 C2 C3 C4 Monomers A1, A2 A1, A2, A4 A1, A4 A2, A4

The copolymers thus obtained were investigated with respect to theresistance thereof to concentrated hydrofluoric acid (49%), an aqueousmixture consisting of hydrochloric acid and hydrogen peroxide (3%hydrogen peroxide), a hydrofluoric acid-neutralizing solution (NH₄HCO₃),and an alkaline developing solution for photoresist (a 2.38% aqueoussolution of TMAH), the results being summarized as follows.

In the case of the copolymer (C1), it was excellent in both hydrofluoricacid resistance and hydrochloric acid resistance. Although thepenetration of the neutralizing liquid was not recognized, it wasimpossible to dissolve the copolymer in the developing solution.

In the case of the copolymer (C2), the penetration of the neutralizingliquid was not recognized. It was found out that in order to obtain acopolymer which was capable of satisfying hydrofluoric acid resistance,hydrochloric acid resistance and alkali-solubility, the mixing ratios ofall of the monomers were required to be adjusted. For example, in orderto provide the copolymer with hydrofluoric acid resistance, the mixingratio of A1 was required to be 50 mol % or more. In order to provide thecopolymer with hydrochloric acid resistance, a total mixing ratio ofA2+A4 was required to be 60 mol % or more. Further, when mixing ratio ofA4 was 30 mol % or more, it was possible to dissolve the resultantcopolymer in the alkaline developing solution in 10 minutes.

In the case of the copolymer (C3), it exhibited a certain degree ofhydrofluoric acid resistance and the penetration of the neutralizingsolution was not recognized. However, it was found poor in hydrochloricacid resistance and was impossible to dissolve the copolymer in thedeveloping solution.

In the case of the copolymer (C4), it was found poor in hydrofluoricacid resistance but was satisfactory in hydrofluoric acid resistance andwas capable of being dissolved in the developing solution.

It was found from the results mentioned above that a resin having themonomer (A1) incorporated therein at a ratio of about 50 mol % wascapable of exhibiting a high hydrofluoric acid resistance. Further, acopolymer having monomers (A1) and (A2) incorporated therein at a ratioof 50:50 (mol/mol) was capable of withstanding in concentratedhydrofluoric acid for 60 minutes. However, the ketone-based acrylicresin decomposed in a strong acid such as hydrochloric acid, thusfailing to exhibit a sufficient degree of hydrochloric acid resistance.

Among the aforementioned copolymers, the copolymers (C2) and (C4)exhibited much possibility of hydrochloric acid resistance and a certaindegree of hydrofluoric acid resistance. As for the combination ofmonomers in these copolymers, it was composed of (A1+)A2+A4.Accordingly, the mixing ratios of these monomers were altered in thesynthesis of these copolymers, and the hydrofluoric acid resistance,hydrochloric acid resistance and alkali-solubility of these copolymerswere investigated to obtain the results shown in FIG. 2.

It was possible, through increasing the mixing ratio of the monomer A1(5-methacryloyloxy-adamantan-2-one), to improve the hydrofluoric acidresistance thereof. If it is desired to meet the specification of: 30minutes in concentrated hydrofluoric acid, the monomer (A1) should beincorporated at a ratio of 50 mol %. However, since this monomer (A1) ispoor in hydrochloric acid/hydrogen peroxide resistance, this monomer(A1) cannot be employed singly. Further, in order to secure a sufficientalkali-solubility, the monomer (A4) which is a segment containingcarboxylic acid should be included at a ratio of 30 mol % or more.

As a result of further studies, it was found that the hydrofluoric acidresistance can be classified into two kinds, i.e. corrosion resistanceto hydrofluoric acid and penetration resistance to hydrofluoric acid.More specifically, there are a couple of corrosion processes when asubstrate is etched using hydrofluoric acid, i.e., a phenomenon whereresin itself is corroded and decomposed; and a phenomenon wherehydrofluoric acid enters into an interface between a substrate and aresin to erode the substrate even though the resin cannot be decomposed.A resin which is widely employed at present in the fine lithography ofelectronic device is novolac. A photoresist to be formed using thisnovolac is satisfactory in corrosion resistance to hydrofluoric acid.However, the photoresist is quite frequently poor in penetrationresistance to hydrofluoric acid. As a result, hydrofluoric acid entersinto an interface between a substrate and the resist film, and tocorrode and peel off the resist film, thereby the substrate is attackedby the hydrofluoric acid.

The acrylic resin mentioned above is sufficiently resistive to thepenetration of hydrofluoric acid into an interface between a substrateand a resin layer. On the other hand, due to the fact that novolacresist is excellent in corrosion resistance to hydrofluoric acid, it isexpected that if a resist film is formed of a 2-ply layer comprising anacrylic resin layer and a novolac resin layer, the resist film would bealso excellent in hydrofluoric acid resistance. In the formation of this2-ply layer, it is conceivable that the acrylic resin layer is employedas a lower layer, on which the novolac resin is coated thereon to forman upper layer.

However, an organic solvent which is generally employed as a resistsolvent dissolves ordinary polymers. Therefore, when a solution ofnovolac resin is spin-coated on an acrylic resin layer, this underlyingacrylic resin would be dissolved by a resist solvent, thus making itimpossible to satisfactorily coat the novolac resin to form a 2-plylayer.

To avoid the aforementioned inconvenience, it is required to select asolvent which is incapable of dissolving the aforementioned acrylicresin but is capable of dissolving novolac resin from the solventsadapted to be employed for photoresist, thereby dissolving the novolacresin. As a sample of acrylic resin, a copolymer comprising 50 mol % ormore of the monomer (A2) and the balance of the monomer (A4) wassynthesized to investigate the solubility of the copolymer to variousresist solvents. As for the resist solvents employed herein, theyincluded ethyl Cellosolve Acetate (ECA), propyleneglycol monomethylether acetate (PGMEA), cyclohexanone, methyl methacrylate (MMA), ethyllactate (EL) and propyleneglycol methyl ether (PGME). The performance ofthese resist solvents was evaluated according to the followingcriterion.

O: It was possible to dissolve the resin, and irregularities of coatingsuch as striation were not recognized on the occasion of spin coating.

X: It was impossible to dissolve the resin, and irregularities ofcoating such as striation were recognized on the occasion of spincoating.

The results obtained are summarized in the Table 5, below.

TABLE 5 ECA X PGMEA X cyclohexanone ◯ MMA X EL ◯ PGME ◯

In the case of cyclohexanone, it took a lot of time in dissolving thecopolymer. In the case of EL, the wettability thereof to a wall surfacewas somewhat poor.

It was found that the copolymer comprising the monomers (A2) and (A4)was incapable being dissolved in PGMEA or MMA as long as the content ofthe monomer (A2) was 50 mol % or more. Namely, as long as the solventfor the resist to be lap-coated is confined to PGMEA or MMA, it ispossible to form a 2-ply structure since the acrylic resin is preventedfrom being dissolved. Especially, since PGMEA is employed widely as asolvent for resists in the market, there are many varieties in theselection of photo resist using PGMEA as a solvent. Therefore, whetheror not the PGMEA can be employed as a solvent for a resist can be easilyconfirmed by watching the catalog thereof or MSDS.

When it is desired to spin-coat the aforementioned acrylic resin, asolvent selected from cyclohexanone, PGME and EL can be employed. In thecases of cyclohexanone and EL however, irregularities of coating calledstriation directed normal to the spinning direction were recognizedafter the spin coating due to somewhat inferior solubility of the resinto these solvents. In view of this, PGME which was excellent in coatingproperties was employed as a solvent for this resin.

The relationships between the three-component system resins formedthrough the copolymerization of the monomers (A2), (A1) and (A4) and theproperties desired to obtain are summarized in FIG. 2. As long as theresin is to be employed singly, it is impossible to obtain a compositionmeeting all of hydrofluoric acid resistance, hydrochloric acid/hydrogenperoxide resistance and alkali-solubility. Supposing that the resistfilm is formed into a 2-ply structure, if the resistance thereof tohydrofluoric acid is entrusted to the upper layer, thus separatelyentrusting the functions thereof to each of the layers, it will berecognized that a solution for obtaining desired properties may be foundin a binary system comprising (A2) and (A4). In this case, it isrequired to select a resin which is capable of forming a 2-ply structureand also capable of exhibiting solubility to a resist solvent.Meanwhile, a resin having a composition satisfying the hydrochloricacid/hydrogen peroxide resistance and alkali-solubility is alreadyknown.

By constructing a resin film into a 2-ply structure with theaforementioned acrylic resin being employed as a lower layer and thenovolac resin as an upper layer, it is possible to provide the resinfilm with resistance to the mixture of hydrochloric acid and hydrogenperoxide, hydrofluoric acid resistance and alkali-solubility. As for thenovolac resin, it is possible to employ cresol novolac or phenolnovolac. When these two kinds of novolac resin were respectively formedinto a film having a thickness of 2 μm and measured with respect to thehydrofluoric acid resistance thereof, a film formed of phenol novolacwas found more excellent in certain degree than a film formed of cresolnovolac. Further, when meta-position novolac resin and para-positionnovolac resin were compared with each other, there was not found anysubstantial difference between them.

If it is tried to secure the alkali-solubility of the acrylic resin in aresin film of 2-ply structure, the resultant resin film would becomehigh in hydrophilicity as a counteraction. As a result, there is muchpossibility that an acid is enabled to penetrate into the resin film. Asa matter of fact, traces where an acid was more or less penetrated intothe resin film were recognized. This problem however can be overcome byslightly enhancing the hydrophobicity of the lower layer.

For example, it was possible to incorporate naphthoquinone diazide(NQD5) as a low molecular compound for enhancing the hydrophobicity intothe lower layer. This compound is generally employed as a photosensitiveagent for a semiconductor resist and is provided, at 5-position thereof,with sulfonate. Since this NQD5 is incapable of exhibitingalkali-solubility unless it is exposed to light, it is assumed that thehydrophobicity of the resin can be enhanced by this NQD5, therebyeffectively preventing an acid from penetrating into the resin layer.When this NQD5 is exposed to light through the irradiation ofultraviolet ray such as g-line of mercury lamp, this NQD5 is changedinto indene carboxylic acid. As a result, the resultant compound isenabled to enhance the alkali-solubility, thereby making it possible todissolve it in an alkaline developing solution. Depending on theexposure wavelength, it is also possible to obtain the same effects asdescribed above even if naphthoquinone diazide provided, at 4-positionthereof, with sulfonate is employed. Further, it is also possible toemploy the following compounds as a compound which is capable ofexhibiting almost the same effects as described above.

As for the examples of solubility-suppressing agent, they includeacid-decomposable compounds which have a sufficient degree ofsolubility-suppressing capability against an alkaline solution and arecapable of producing an acid-decomposed material which is capable ofgenerating —O— in an alkaline solution.

Examples of the solubility-suppressing agent useful herein includeisopropyl carbonyl ester, tetrahydropyranyl carbonyl ester,tetrahydrofuranyl carbonyl ester, methoxyethoxymethyl carbonyl ester,2-trimethylsilylethoxymethyl carbonyl ester, t-butyl carbonyl ester,trimethylsilyl carbonyl ester, triethylsilyl carbonyl ester,t-butyldimethylsilyl carbonyl ester, isopropyldimethylsilyl carbonylester and di-t-butylmethylsilyl carbonyl ester of polycarboxylic acid ofcondensed polycyclic (alicyclic or aromatic) compound; oxazole;2-alkyl-1,3-oxazoline; 4-alkyl-5-oxo-1,3-oxazoline; and5-alkyl-4-oxo-1,3-dioxorane.

Further, it is also possible to employ the following compounds:

It was possible, through the addition of NQD5 to acrylic resin at aratio of not less than 10% by weight, to enhance the hydrophobicity ofthe lower layer, thereby preventing an acid from penetrating into thelower layer. Moreover, the alkali-solubility of the acrylic resin wasnot obstructed at all by the addition of the NQD5. When the mixing ratioof the NQD5 was altered to 10% by weight, 20% by weight and 30% byweight, it was found that the degree of improvement of the acrylic resincould not be enhanced any more even if the mixing ratio of the NQD5 wasincreased over 20% by weight. Further, even if the mixing ratio of theNQD5 was increased up to 50% by weight, it was possible to spin-coat theacrylic acid solution. However, when the mixing ratio of the NQD5 wasincreased higher than 50% by weight, it was found impossible to coat theacrylic resin solution due to the decrease in content of the resincomponent. In view of these facts, it is assumed that a mixing ratio ofnot more than 20% by weight of the NQD5 would be enough for improvingthe acrylic resin.

It was found possible to substantially achieve the requirements to meetthe specifications demanded in the frost treatment by using a laminatefilm comprising a lower layer which is composed of acrylic resin formedthrough the copolymerization of the monomers (A2) and (A4), and an upperlayer which is composed of novolac resist. In order to find out afurther optimized composition, various copolymers were synthesized bychanging the mixing ratio of the monomer (A2) as shown in Table 6,below.

TABLE 6 Copolymers C5 C6 C7 C8 C9 C10 Ratio of copolymer 30 40 50 60 7080 (A2) (mol %)

After the NQD5 was added to each of the copolymers at a ratio of 5 to20% by weight, the resultant mixtures were respectively dissolved inPGME. Each of the solutions thus obtained was coated on galliumphosphide substrate by spin coating meathod to form a lower resin layer.Then, novolac resist (S1818, Shiplay) was coated on the lower resinlayer by spin coating method to form an upper resin layer having athickness of 2 μm, thereby manufacturing samples each having aprotective film.

The samples thus obtained were examined by subjecting them to a processwhich was expected to be performed in the frost treatment. In thisprocess, the samples were immersed for 30 minutes in an aqueous solutionof hydrochloric acid/hydrogen peroxide (hydrochloric acid:hydrogenperoxide:water=95:2:3 (based on volume)). Under this condition, severalsamples were drawn out and the protective films were removed by using analkaline developing solution for semiconductor device (AD-10: a 2.38%aqueous solution of TMAH). When the substrates were observed by using ascanning electronic microscope, it was confirmed that the burr of thesubstrates was removed and the sidewalls of the substrates were neatlyflattened. It was found out from the aforementioned results that theprotective films created as described above were useful as a protectivefilm for an etching solution comprising hydrochloric acid and hydrogenperoxide. It was also found out from the results of this experiment thatif the mixing ratio between the monomer (A2) and the monomer (A4) wasconfined within the range of 20:80-80:20 in the preparation of acopolymer, it was possible to secure a sufficient resistance against anetching solution comprising hydrochloric acid and hydrogen peroxide byusing only the copolymer without accompaniment of the novolac resist.

The residual samples which were not drawn out were immersed for 30minutes in hydrofluoric acid (49%, room temperature) and then furtherimmersed for 10 minutes in a neutralizing solution (aqueous solution ofNH₄HCO₃). Subsequently, the cleavage surface of the samples was observedby cross-sectional SEM.

As a result, it was confirmed that in the cases of copolymers (C5) and(C6), the resin film formed on the substrate was fractured. The reasonfor this may be attributed to the fact that since the polymer employedas the lower layer was eroded by the acid and part of the lower layerwas scooped out, resulting in the collapsing of the upper layer. Oncethe collapsing of the upper layer occurs, the acid enters into theinside of resin film. As a result, even a portion located inner than thedesigned dimension erode, thus defects generate in the substrate.Furthermore, the resin which was eluted out on the occasion of etchingusing hydrofluoric acid was permitted to readhere onto the galliumphosphide substrate, thus preventing the frost from neatly forming at aninner region located several micrometers as measured from the uppersurface of the substrate.

In the cases of the copolymers (C7), (C8), (C9) and (C10), thephenomenon described above was not observed, thus the frost was formedneatly. On the upper surface of the substrate, there was left remainedthe resin which endured against the erosion to be effected by the acidduring the etching process. Since the gallium phosphide was eroded to anextent of 10 μm or so under the aforementioned condition, a portion ofthe substrate which was located immediately below the resin which wasnot eroded was turned into an eaves-like configuration.

Further, the resin layer of each of the samples was removed by using analkaline developing solution (AD-10: Tama Chemicals co.: a 2.38% aqueoussolution of TMAH) and the cleavage surface of the samples was observedby cross-sectional SEM.

In the cases of the copolymers (C5) and (C6), a portion which was closeto the top surface thereof was etched insufficiently. Other samples wereall etched uniformly. Incidentally, if hydrofluoric acid penetrates intothe top surface of sample, defects called pit may generate. However, thegeneration of such a pit was not observed on the surface which wasexposed by the peeling of the protective film in any of all samples,indicating that the penetration of hydrofluoric acid from the topsurface of the protective film was prevented.

In order to secure a sufficient acid etching resistance of the resin,the copolymers comprising the components (A2) and (A4) according to oneembodiment of the present invention were formulated such that the lowerlimit of the mixing ratio of the component (A2) was set to 40 mol % ormore. As already explained above, in order to secure thealkali-solubility of the resin, the mixing ratio of the component (A4)is required to be 30 mol % or more. Namely, if the mixing ratio of thecomponent (A2) is more than 70 mol %, it may become difficult to easilyremove the resin by using an alkaline developing solution after theetching treatment thereof. When the alkali-solubility of the resin istaken into account, the mixing ratio of the component (A2) in thecopolymer should preferably be 60 mol % or less.

Furthermore, the weight average molecular weight (Mw) of resin is alsoan important condition influencing the alkali-solubility of resin. Ifthis Mw is less than ten thousands, the resin dissolves in hydrofluoricacid, thereby making it difficult to generate frosting in the galliumphosphide substrate. On the other hand, if this Mw is higher than thirtythousands, it may become difficult to remove the resin layer by using analkaline developing solution. As far as the alkali-solubility isconcerned, the increase of Mw of the copolymer acts in the same manneras the mixing ratio of the component (A2). With respect to the influenceof Mw on the hydrofluoric acid resistance however, the hydrofluoric acidresistance of the copolymer tends to be influenced in somewhat differentmanner.

By taking the aforementioned results into account, the resin layer wasformed into a 2-ply structure wherein the upper layer is provided withcorrosion resistance to hydrofluoric acid and the lower layer isprovided with resistance to the penetration of hydrofluoric acid, thusseparately entrusting the functions thereof to these layers. By doingso, it was possible to meet the specifications required for the frosttreatment of the resin layer.

The resin layer having such a 2-ply structure was capable ofwithstanding the corrosion in an aqueous solution of hydrochloricacid/hydrogen peroxide for 60 minutes and in a hydrofluoric acid for 60minutes, and was also capable of dissolving in an alkaline developingsolution (a 2.38% aqueous solution of TMAH) within about one minute.

Next, the present invention will be further explained in detail withreference to specific embodiments.

FIG. 3 shows a cross-sectional view of a light emitting element whichwas manufactured by the method according to one embodiment of thepresent invention. As shown in FIG. 3, on a compound semiconductorsubstrate 10 having an electrode 17 on the bottom surface thereof, thereare formed a light emitting layer 14 and a current diffusion layer 15,which are successively deposited thereon by epitaxial growth. On thecurrent diffusion layer 15, there is additionally formed a wiringelectrode pattern 16. These light emitting layer 14 and currentdiffusion layer 15 will be hereinafter referred to integrally as anepitaxial layer 18.

As for the compound semiconductor substrate 10, it is possible to employn-GaAs or n-GaP. The light emitting layer 14 comprises a lower cladlayer 11 made of n-InAlP, on which an active layer 12 made of InGaAlPand an upper clad layer 13 made of p-InAlP are deposited to form ahetero-structure. The current diffusion layer 15 may be formed usingp-GaP for instance.

In this embodiment, although an n-type substrate is shown as an example,it is also possible to employ a p-type substrate. If a p-type substrateis to be employed, the conductivity type of each of the layers should besimply reversed.

Since the light emitting element was manufactured by the methodaccording to the embodiment of the present invention, it was possible toform a rugged surface 19 by frost treatment on the sidewall of thecompound semiconductor substrate 10.

Specifically, the light emitting element shown in FIG. 3 wasmanufactured according to the following method by using an acid etchingresistance material according to one embodiment of the presentinvention. Namely, the material employed herein was formed of acopolymer comprising 60 mol % of the aforementioned monomer (A2) and 40mol % of the aforementioned monomer (A4). The NMR chart of thiscopolymer is shown in FIG. 4. Naphthoquinone diazide was incorporated inthis copolymer at a ratio of 10% by weight and then dissolved in PGME toprepare a solution for forming a protecting film.

Next, the method of manufacturing a semiconductor device according toone embodiment of the present invention will be explained with referenceto FIGS. 5 to 12.

First of all, as shown in FIG. 5, on the surface of a compoundsemiconductor substrate 10 having electrodes 17 on the bottom surfacethereof, there were formed an epitaxial layer 18 and electrodes 16.Although not shown in FIG. 5, the epitaxial layer 18 was constituted bythe light emitting layer 14 consisted of the lower clad layer 11, theactive layer 12 and the upper clad layer 13, and by the currentdiffusion layer 15 as explained with reference to FIG. 3. In thisepitaxial layer 18, grooves 20 were formed in such a manner that thegrooves 20 were located on the outer circumference of the electrodes asshown in FIG. 6.

Then, as shown in FIG. 7, a protecting film 21 was formed on theepitaxial layer 18 so as to cover the electrodes 16. The formation ofthe protecting film 21 was performed as follows. First of all, theaforementioned solution for forming the protecting film was coated onthe epitaxial layer 18 by spin coating method and the resultant film waspre-baked for 90 seconds at a temperature of 120° C. to remove thesolvent, thereby forming a lower resin layer having a thickness of 0.3μm. On this lower resin layer, novolac resist (S1818, Shiplay) wasfurther coated and pre-baked for 90 seconds at a temperature of 110° C.to vaporize the solvent, thereby forming an upper resin layer having athickness of 2.5 μm. As a result, a resin layer of 2-ply structure wasformed, thus enabling it to be used as a protecting film 21 for an acid.

After finishing the formation of the protecting film 21, the substrate10 was subjected to dicing treatment to form a cut line 22 penetratinginto a midway in thickness of the substrate 10 as shown in FIG. 7. Then,the substrate 10 was turned upside down and a protecting film 23 wasformed on the rear side of the substrate 10 in the same manner asdescribed above, thereby covering the electrodes 17 as shown in FIG. 8.Subsequently, as shown in FIG. 9, the protecting film 21 was adheredonto an expand sheet 24 and the substrate 10 was subjected to dicingtreatment from the protecting film 23 side to form a cut line 25.Subsequently, the expand sheet 24 was stretched to separate thesubstrate 10 into individual chips.

These chips were then immersed in a mixed solution containinghydrochloric acid and hydrogen peroxide to remove fractured layers.Subsequently, these chips were immersed in 49% concentrated hydrofluoricacid to perform the frost treatment thereof. As a result, a ruggedsurface 19 was formed on the sidewalls of the chips as shown FIG. 10.After being neutralized using a hydrofluoric acid-neutralizing liquid,the chips were treated with an aqueous solution of TMAH to dissolve andremove the protecting film 23, thereby enabling the electrodes 17 toexpose as shown in FIG. 11. On this occasion, part of the protectingfilm 21 was also removed.

Finally, the electrodes 17 were adhered onto the resin sheet 26 toremove the residual portion of the protecting film 21 to obtain astructure as shown in FIG. 12. Then, the chips were individually takenoff from the resin sheet 26 to accomplish the manufacture of a lightemitting element (light emitting diode) having, on the sidewalls ofsubstrate, the rugged surface as shown in FIG. 3.

On the other hand, by following the same process as explained aboveexcept that the aforementioned rugged surface was not formed on thesidewalls of substrate, light emitting diodes according to the prior artwere manufactured and compared, with respect the luminance, with thelight emitting diodes prepared as described above according to oneembodiment of the present invention. As a result, the luminance of thelight emitting diode provided with the rugged surface was found enhancedby 40% in average of ten pieces as compared with the light emittingdiode of the prior art.

Further, by following the same process as explained above except thatonly the conventional novolac resist (S1818) was employed as aprotecting film, light emitting diodes were manufactured. As a result,hydrofluoric acid penetrates into the protecting film on the occasion ofhydrofluoric acid treatment, resulting in the erosion of the lightemitting layer by the effect of the hydrofluoric acid. As a result, thepercent defective was as high as 30% or more.

Whereas, in the case of the light emitting elements manufactured by themethod according to one embodiment of the present invention, the percentdefective was as very low as 0.1% or less. In addition to the prominentdecrease of the percent defective, it was confirmed through theobservation of the optical microscopic images as well as through theobservation of the SEM images that as compared with the conventionallight emitting elements, the light emitting elements manufactured by themethod according to one embodiment of the present invention were alsoimproved in configuration as acceptable products.

According to one embodiment of the present invention, there is alsoprovided an acid etching resistance material which is adapted to beemployed in a frost treatment for enhancing the light extractingefficiency of light emitting element, and is capable of exhibitingsufficient acid resistance and excellent alkali-solubility. Further,according to another embodiment of the present invention, there is alsoprovided a method of manufacturing a semiconductor device where theaforementioned acid etching resistance material is employed.Furthermore, according to a further embodiment of the present invention,there is also provided a novel copolymer.

Embodiment 2

Next, the features of this embodiment will be explained with referenceto the attached drawings. Incidentally, the components which are commonthroughout the embodiments will be identified by the attaching the samereference symbols, thereby omitting the overlapped explanation thereof.Further, each of the drawings is a schematic view only for the purposeof explanation and understanding of the invention, so that theconfiguration, size and proportion thereof may differ depending on thelocation thereof from the actual apparatus. However, they may beoptionally modified in design by referring to the following explanationsas well as to the known techniques.

The acid etching resistance material according to this embodiment shouldbe a photosensitive hydrofluoric acid etching material havingphotosensitivity. By the term “photosensitive hydrofluoric acid etchingmaterial”, it is intended to mean a material which is applicable tohydrofluoric acid etching and is provided with photosensitivity. Thisphotosensitive hydrofluoric acid etching material is characterized inthat it comprises a resin, and a photoacid generating agent which iscapable of generating acid as it is exposed to light. Next, these resinand photoacid generating agent as well as other compounds will beexplained in detail.

1) Resin:

The resin according to this embodiment is featured to have at least twokinds of repeating units (hereinafter, referred to as segments) whichcan be represented by the following general formula (PS1). For theconvenience of explanation, the resin will be explained segment bysegment, i.e., a first segment comprising a main chain and R¹², and asecond segment comprising a main chain and R¹⁴. Incidentally, the firstsegment and the second segment are incorporated at random in the mainchain.

(in the general formula (PS1), R¹¹ and R¹³ are individually a hydrogenatom or methyl group; R¹² is selected from the group consisting ofadamantane, tricyclodecane, norbornane, isobornane, cyclohexane andcyclooctane, each having one or two hydroxyl groups; R¹⁴ is selectedfrom the group consisting of adamantane, tricyclodecane, norbornane,isobornane, cyclohexane and cyclooctane, each having one ketone groups;and m and n represent individually a natural number).

The main chain is either acrylate where R¹¹ and R¹³ are both constitutedby a hydrogen atom, or methacrylate where R¹¹ and R¹³ are bothconstituted by methyl group. The acrylic resin provided with theseacrylic backbones is more excellent in hydrofluoric acid resistance ascompared with a resin having other kinds of main chain.

In viewpoint of improving the resolution on the occasion of opticalpatterning, it is more preferable to employ acrylate where R¹¹ and R¹³are both constituted by hydrogen atom.

The first segment comprises tertiary carbon atom, and an alicyclic groupR¹² which is linked via this tertiary carbon atom to the main chain andprovided with a substituent group to be discussed hereinafter. Thisfirst segment is a solubility-suppressing group (inhibitor group,protecting group) against an alkaline developing solution and is capableof improving the resolution.

Due to the fact that tertiary carbon atom is interposed between thealicyclic group and the main chain, this first segment can bedissociated and decomposed to generate carboxylic acid under a heatedcondition where a strong acid is employed as a catalyst. Due to thedecomposition reaction of side chain of this first segment, the resinaccording to this embodiment is enabled to dissolve in an alkalinedeveloping solution. Due to this characteristic, the resin according tothis embodiment can be employed as a photosensitive hydrofluoric acidetching resist material. Incidentally, the acid to be employed as acatalyst can be generated by exposing the photoacid generating agent tolight.

The alicyclic group constituting R¹² may be selected from the groupconsisting of adamantane, tricyclodecane, norbornane, isobornane,cyclohexane and cyclooctane. Since these alicyclic groups are bulky,they are capable of protecting the main chain from hydrofluoric acid,thereby enhancing hydrofluoric acid corrosion/decomposition resistance.Incidentally, since adamantane, tricyclodecane, norbornane andisobornane are formed of a crosslinking structure and hence rigid, thehydrofluoric acid corrosion/decomposition resistance of the resin can befurther enhanced.

In viewpoint of enhancing the hydrofluoric acid corrosion/decompositionresistance, the employment of adamantane which is most rigid and formedof a chemically stable structure is more preferable.

The substituent group attached to the R¹² is provided with one or twohydroxyl groups. Hydroxyl group is excellent in adhesion to a substrate,thus enhancing the hydrofluoric acid penetrating resistance.Incidentally, if there are three or more hydroxyl groups in thesubstituent group, the hydrophilicity of resin is further enhanced toextremely increasing the solubility of resin to alkaline developingsolution. As a result, the formation of pattern would become difficultin the optical patterning step, greatly deteriorating the resolution onthe occasion of optical patterning. Therefore, the inclusion of three ormore hydroxyl groups in the substituent group is not preferable.

When the balance between the solubility to the alkaline developingsolution and the adhesion to substrate is taken into account, theinclusion of only one hydroxyl group in the substituent group is mostpreferable.

The second segment is composed of an alicyclic group R¹⁴ which isprovided with a substituent group to be discussed hereinafter. Thissecond segment is capable of enhancing the hydrofluoric acid resistanceof resin.

The alicyclic group constituting R¹⁴ has characteristics which aresimilar to those of R¹². Further, when R¹⁴ is constituted by a groupwhich is similar to that of R¹², the polymerization of the resin wouldbecome easier, thus making it more preferable.

The substituent group attached to the R¹⁴ is provided with one ketonegroup. As compared with hydroxyl group, the ketone group is moreexcellent in adhesion to a substrate, thus enhancing the hydrofluoricacid penetrating resistance. Incidentally, if there are two or moreketone groups in the substituent group, the polymerization of monomersto be employed as raw materials of the resin would become moredifficult. Therefore, the inclusion of two or more ketone groups in thesubstituent group is not preferable.

Incidentally, the employment, for example, of carboxylic acid group as asubstituent group is not suitable due to the facts that it is low inhydrofluoric acid resistance, that it is high in polarity and hence poorin solubility to ordinary resist solvents, and that it is excessivelyhigh in hydrophilicity, hence greatly deteriorating the resolution onthe occasion of optical patterning. Further, the employment of lactonegroup as a substituent group is not suitable due to the facts that whenlactone group is reacted with an acid or alkali, lactone group splits togenerate carboxylic acid, thereby deteriorating the hydrofluoric acidresistance.

With respect to the ratio between the first segment and the secondsegment, the ratio of m:n should preferably be confined within the rangeof 30:70 to 70:30. As long as the ratio of m:n is confined within thisrange, the functions of each of these segments would be effectivelyexhibited. Namely, if m is 30 or more, the resolution would be enhancedon the occasion of optical patterning, and if n is 30 or more, thehydrofluoric acid resistance would be enhanced.

Incidentally, when the solubility of resin on the occasion of developingstep is taken into consideration, the upper limit of molecular weight ofthe resin would be about 100,000, more preferably about 40,000 to 50,000in order to retain the resolution of the order of microns.

As explained above, since the resin according to this embodiment isprovided with excellent hydrofluoric acid resistance and excellentphotosensitivity, the resin can be employed as a photosensitivehydrofluoric acid etching resist material.

Further, since the resin according to this embodiment is composed of atleast two kinds of segments, it is preferable in the respects that thepolymerization thereof would be facilitated, and that the selection ofalicyclic groups as well as composition ratio can be easily optimizeddepending on the applications of the resin.

Furthermore, since the resin according to this embodiment does notinclude therein a double bond of carbon-carbon, there will be no lightabsorption by π-electron cloud, so that the resin is excellent intransparency in all of the ultraviolet, visible and infrared regions,i.e. in the wavelength region ranging from around 190 nm to around 1 μm.Therefore, the resin according to this embodiment can be employed, as itis, as an optical component of photochemical semiconductor devices suchas an optical waveguide, etc.

The resin according to this embodiment can be synthesized according tothe flowchart shown in FIG. 13 for instance.

2) Photoacid Generating Agent:

Photoacid generating agent (PAG) may be selected from any kinds ofcompounds as long as they are capable of generating an acid as they areexposed to light.

For example, it is possible to employ aryl onium salts, naphthoquinonediazide compounds, diazonium salts, sulfonate compounds, sulfoniumcompounds, sulfamide compounds, iodonium compounds, sulfonyldiazomethane compounds, etc.

Specific examples of the aforementioned compounds includetriphenylsulfonium triflate, diphenyliodonium triflate,2,3,4,4-tetrahydroxybenzophenone-4-naphthoquinone diazide sulfonate,4-N-phenylamino-2-methoxyphenyl diazonium sulfate,4-N-phenylamino-2-methoxyphenyldiazonium-p-ethylphenyl sulfate,4-N-phenylamino-2-methoxyphenyldiazonium-2-naphthyl sulfate,4-N-phenylamino-2-methoxyphenyldiazonium-phenyl sulfate,2,5-diethoxy-4-N-4′-methoxyphenylcarbonylphenyldiazonium-3-carboxy-4-hydroxyphenylsulfate, 2-methoxy-4-N-phenylphenyldiazonium-3-carboxy-4-hydroxyphenylsulfate, diphenylsulfonyl methane, diphenylsulfonyl diazomethane,diphenyl disulfone, α-methylbenzoin tosylate, pyrogallo trimesylate,benzoin tosylate, MPI-103 (CAS.NO. [87709-41-9]; Midori Kagaku Co.,Ltd.), BDS-105 (CAS.NO. [145612-66-4]; Midori Kagaku Co., Ltd.), NDS-103(CAS.NO. [110098-97-0]; Midori Kagaku Co., Ltd.), MDS-203 (CAS.NO.[127855-15-5]; Midori Kagaku Co., Ltd.), Pyrogallo tritosylate (CAS.NO.[20032-64-8]; Midori Kagaku Co., Ltd.), DTS-102 (CAS.NO. [75482-18-7];Midori Kagaku Co., Ltd.), DTS-103 (CAS.NO. [71449-78-0]; Midori KagakuCo., Ltd.), MDS-103 (CAS.NO. [127279-74-7]; Midori Kagaku Co., Ltd.),MDS-105 (CAS.NO. [116808-67-4]; Midori Kagaku Co., Ltd.), MDS-205(CAS.NO. [81416-37-7]; Midori Kagaku Co., Ltd.), BMS-105 (CAS.NO.[149934-68-9]; Midori Kagaku Co., Ltd.), TMS-105 (CAS.NO. [127820-38-6];Midori Kagaku Co., Ltd.), NB-101 (CAS.NO. [20444-09-1]; Midori KagakuCo., Ltd.), NB-201 (CAS.NO. [4450-68-4]; Midori Kagaku Co., Ltd.),DNB-101 (CAS.NO. [114719-51-6]; Midori Kagaku Co., Ltd.), DNB-102(CAS.NO. [131509-55-2]; Midori Kagaku Co., Ltd.), DNB-103 (CAS.NO.[132898-35-2]; Midori Kagaku Co., Ltd.), DNB-104 (CAS.NO. [132898-36-3];Midori Kagaku Co., Ltd.), DNB-105 (CAS.NO. [132898-37-4]; Midori KagakuCo., Ltd.), DAM-101 (CAS.NO. [1886-74-4]; Midori Kagaku Co., Ltd.),DAM-102 (CAS.NO. [28343-24-0]; Midori Kagaku Co., Ltd.), DAM-103(CAS.NO. [14159-45-6]; Midori Kagaku Co., Ltd.), DAM-104 (CAS.NO.[130290-80-1] and CAS.NO. [130290-82-3]; Midori Kagaku Co., Ltd.),DAM-201 (CAS.NO. [28322-50-1]; Midori Kagaku Co., Ltd.), CMS-105 (MidoriKagaku Co., Ltd.), DAM-301 (CAS.NO. [138529-81-4]; Midori Kagaku Co.,Ltd.), SI-105 (CAS.NO. [34694-40-7]; Midori Kagaku Co., Ltd.), NDI-105(CAS.NO. [133710-62-0]; Midori Kagaku Co., Ltd.); and EPI-105 (CAS.NO.[135133-12-9]; Midori Kagaku Co., Ltd.).

Further, as the photoacid generating agent, the following compounds canbe also employed.

wherein X⁻ is CF₃SO₃ ⁻, BF₄ ⁻, AsF₆ ⁻, PF₆ ⁻ or SbF₆ ⁻.

wherein Z is alkyl group.

Among these photoacid generating agents, preferable examples thereof aretriphenylsulfonium triflate, diphenyliodonium triflate,trinaphthylsulfonium triflate, dinaphthyliodonium triflate,dinaphthylsulfonyl methane, NAT-105 (CAS.NO. [137867-61-9]; MidoriKagaku Co., Ltd.), NAT-103 (CAS.NO. [131582-00-8]; Midori Kagaku Co.,Ltd.), NAI-105 (CAS.NO. [85342-62-7]; Midori Kagaku Co., Ltd.), TAZ-106(CAS.NO. [69432-40-2]; Midori Kagaku Co., Ltd.), NDS-105 (Midori KagakuCo., Ltd.), PI-105 (CAS.NO. [41580-58-9]; Midori Kagaku Co., Ltd.),s-alkylated dibenzothiophene triflate, and s-fluoroalkylateddibenzothiophene triflate (Daikin Co., Ltd.). Among these photoacidgenerating agents, especially preferable examples thereof aretriphenylsulfonium triflate, trinaphthylsulfonium triflate,dinaphthyliodonium triflate, dinaphthylsulfonyl methane, NAT-105(CAS.NO. [137867-61-9]; Midori Kagaku Co., Ltd.), NDI-105 (CAS.NO.[133710-62-0]; Midori Kagaku Co., Ltd.), and NAI-105 (CAS.NO.[85342-62-7]; Midori Kagaku Co., Ltd.).

In this embodiment, a preferable mixing ratio of the photoacidgenerating agent is confined within the range of 0.001 to 50 mol %, morepreferably 0.01 to 40 mol %, most preferably 0.1 to 20 mol % based on atotal quantity of solid matters. Namely, if the mixing ratio of thephotoacid generating agent is less than 0.001 mol %, it would bedifficult to form a pattern with high resolution. On the other hand, ifthe mixing ratio of the photoacid generating agent is more than 50 mol%, the film to be formed would be deteriorated in mechanical strengththereof.

3) Others:

The photosensitive hydrofluoric acid etching resist materials accordingto this embodiment can be prepared as varnish by dissolving thesecompounds in an organic solvent and filtering the resultant solution.

As for the organic solvent, it is possible to employ ketone-basedsolvents such as cyclohexanone, acetone, methylethyl ketone,methylisobutyl ketone, etc.; cellosolve-based solvents such as methylcellosolve, methyl cellosolve acetate, ethyl cellosolve acetate, butylcellosolve acetate, etc.; ester-based solvents such as ethyl acetate,butyl acetate, isoamyl acetate, γ-butyrolactone, etc.; glycol-basedsolvents such as propylene glycol monomethyl ether acetate, etc.;nitrogen-containing solvents such as dimethylsulfoxide, hexamethylphosphoric triamide dimethylformamide, N-methylpyrrolidone, etc.; andmixed solvents comprising any one of the aforementioned solvents, towhich dimethyl sulfoxide, dimethylformaldehyde or N-methylpyrrolidinoneis added.

It is also possible to preferably employ, as the organic solvent,propionic acid derivatives such as methyl methylpropionate, etc.;lactates such as ethyl lactate, etc.; and PGMEA (propyleneglycolmonomethylether acetate) since these compounds are low in toxicity.

Incidentally, these organic solvents may be employed singly or incombination of two or more. Further, these organic solvents may containaliphatic alcohol such as isopropyl alcohol, ethyl alcohol, methylalcohol, butyl alcohol, n-butyl alcohol, s-butyl alcohol, t-butylalcohol, isobutyl alcohol, etc.; and aromatic solvent such as toluene,xylene, etc.

The photosensitive hydrofluoric acid etching resist materials mayfurther contain an alkali-soluble resin for enhancing the solubilitythereof to an alkaline developing solution in the developing step; aresinous compound which is capable of enhancing the solubility to analkaline developing solution as it is irradiated with radiation whichwill be effected for the purpose of enhancing the resolution at the timeof optical patterning; a solubility inhibitor for decreasing thesolubility of resin to alkaline developing solution in the developingstep; a crosslinking agent for retaining the configuration of pattern ofphotosensitive hydrofluoric acid etching resist material after theoptical patterning step; a surfactant for modifying the coated film; oran amine additive for preventing the deactivation of the acid generatedin an optical reaction.

The photosensitive hydrofluoric acid etching resist materials accordingto this embodiment can be applied to the manufacture of semiconductordevices. The semiconductor device herein means a device which isprovided with a single body or compound of semiconductor element andwhich can be manufactured by using fine fabrication techniques. Morespecifically, the semiconductor device herein means a device to whichoptical pattern etching by hydrofluoric acid etching is suitablyapplicable. This optical pattern etching will be explained below in moredetail.

This optical pattern etching is performed by a process comprising aresist coating step, an exposure step, a heating step, a developing stepand an etching step using hydrofluoric acid.

First of all, in the resist coating step, a layer of a photosensitivehydrofluoric acid etching resist material according this embodiment isformed on the substrate made of semiconductor or quartz glass by spincoating method, etc. Herein, quartz glass means a high-purity quartzglass which can be worked by using fine fabrication technique.Generally, this kind of quartz glass may contain as an impurity metalelements each at a ratio of 1 ppb at most.

Next, in the photo-exposure process (PEP) step, the layer of thephotosensitive hydrofluoric acid etching resist material is irradiated,through a desired pattern, with light of desired pattern. In thisexposure step, acid generates due to the employment of a photoacidgenerating agent.

Next, in the post-exposure bake (PEB) step, heat is applied to asubstrate. In this heating step, in the exposed portions where acidcatalyst generates in the previous step, the tertiary carbon atomexisting between the alicyclic group R¹² and the main chain isdecomposed and carboxylic acid is generated. Due to the decompositionreaction of this first segment, a portion of the photosensitivehydrofluoric acid etching resist material which is located in theexposed regions changes the solubility thereof from alkali-insoluble toalkali-soluble. Incidentally, the heating temperature (PEB temperature)in this heating step should preferably be confined within the range of100° C. to 160° C., and heating time should preferably be confinedwithin the range of 80 seconds to 100 seconds. In order to enable thedissociation reaction to take place within several minutes in this PEB,a temperature of 100° C. or more is required. On the other hand, whenthe temperature is raised more than 160° C., the dissociation reactiontakes place without necessitating the presence of acid, thereby makingit difficult to perform the patterning.

Next, in the developing step, the substrate is immersed in an alkalinedeveloping solution. In this developing step, a portion of thephotosensitive hydrofluoric acid etching resist material which islocated in the exposed regions dissolves. With respect to theconcentration of the alkaline developing solution, in the case oftetrahydroammonium hydroxide (TMAH) developing solution which isgenerally employed for semiconductor resists, the concentration of TMAHshould preferably be confined within the range of 0.05% to 0.5%, morepreferably around 0.12%. Since the concentration of the TMAH developingsolution is 2.38% in general, it is possible to obtain a developingsolution of desired concentration by diluting this TMAH developingsolution with as about 20 times as large volume of water. The period oftime required for the development using the TMAH developing solution ofthis desired concentration would be within the range of 30 seconds to 90seconds. However, the actual period of time should be adjusted dependingon the concentration of the TMAH developing solution.

Next, in the etching step, the substrate is immersed in a solutioncontaining hydrofluoric acid at a concentration ranging from 30% to 50%.By employing an etching solution containing hydrofluoric acid at aconcentration of 30% or more, the period of this immersion step would beprominently shortened. Incidentally, the stock solution of hydrofluoricacid generally contains hydrofluoric acid at a concentration rangingfrom 46 to 50% (see Dictionary of Physics and Chemistry; Iwanami BookCo., Ltd.). In this etching step, a portion of the substrate which wasexposed to light is etched away.

Finally, on the occasion of removing the resist, the substrate isentirely exposed to light and then immersed in an alkaline developingsolution to remove the photosensitive hydrofluoric acid etching resistmaterial.

As for the substrate, it is possible to employ a semiconductorsubstrate, a quartz glass substrate, etc.

As for the specific examples of the semiconductor substrate, theyinclude compound semiconductors such as GaP, GaAs, GaAsP, AlGaAs,InGaAsP, GaInAlP, InP, etc.; as well as elemental semiconductors such asSi, Ge, etc.

If a quartz glass substrate is to be employed, it is preferable to applyan anti-reflection lower film to the bottom surface of substrate inorder to suppress the reflection of light at the bottom surface of thesubstrate.

As explained above, since the photosensitive hydrofluoric acid etchingresist material according to this embodiment is employed, it is possibleto perform the etching using a solution containing hydrofluoric acid ata high concentration. As a result, the time period required for theoptical patterning etching step can be shortened.

Further, the photosensitive hydrofluoric acid etching resist materialaccording to this embodiment can be applied to the manufacture of thesemiconductor devices as explained below. For example, this etchingmaterial can be applied to the manufacturing method which comprises:forming a sacrificial layer made of quartz glass on the semiconductorsubstrate; forming an element structure made of semiconductor on thesacrificial layer; forming a portion made of a material which is poor inhydrofluoric acid resistance on the semiconductor substrate;subsequently covering the portion made of a material which is poor inhydrofluoric acid resistance by using the photo-sensitive hydrofluoricacid etching material according to this embodiment; and subsequentlyremoving the sacrificial layer by applying a hydrofluoric acid solutionto the semiconductor substrate.

Next, an optical scanning apparatus representing one example of thesemiconductor device according to one embodiment of the presentinvention will be explained in detail. First of all, one example of theoptical scanning apparatus will be explained with reference to FIGS.14A, 14B and 15.

FIG. 14A is a top view schematically illustrating the optical scanningapparatus. FIG. 14B is an enlarged view schematically illustrating anencircled region of FIG. 14A. FIG. 15 is a cross-sectional viewschematically illustrating the central axis of the beam-like structure111 of the optical scanning apparatus.

As shown in FIGS. 14A and 14B, the scanning beam is emitted from a lightsource 116, then passes through an optical waveguide structure 115 forguiding the beam and through a beam-condensing structure 119, andthereafter is emitted out of the light emitting end 117 of the opticalwaveguide, which is located at an distal end of the beam-like structure111.

A tandem gear type driving mechanism 112 is employed for generatingpower for driving the beam-like structure 111. There is provided acoupling structure 118 for coupling the beam-like structure with thedriving mechanism, the coupling structure 118 being constituted by astabilizing spring structure 113, a bellows-like spring structure 114and a beam structure linking them to each other.

The optical scanning apparatus constructed in this manner is operatedsuch that the beam-like structure 111 is vibrated to vibrate also thelight emitting end 117 of the optical waveguide to enable the beam fromthe light source 116 to perform the scanning. The beam vibratingdirection 120 shown by an arrow in FIG. 14B indicates the direction ofthe scanning beam to be operated by this apparatus.

As shown in FIG. 15, an SOI substrate 121 constituting the substrate ofthe element structure is constituted by a laminate structure comprising,when mentioned from below, a Si substrate 2101, a SiO₂ layer 2102 and aSi active layer 2103. On this SOI substrate 121, there are disposed theaforementioned light source 116, the beam-condensing structure 119 andthe optical waveguide structure 115.

In the case of this optical scanning apparatus, the optical waveguidestructure 115 is formed of a material exhibiting a low hydrofluoric acidresistance, and the step of performing the hydrofluoric acid etching isutilized in the step of manufacturing a movable portion (for example,the beam-like structure 111) of the element structure, i.e. the step ofremoving the SiO₂ layer 2102 to be used as a sacrificial layer.

Next, the method of manufacturing the optical scanning apparatus shownin FIGS. 14A, 14B and 15 will be explained.

First of all, after the fabrication of the optical waveguide structure115 on the SOI substrate, the element structure is formed.

Thereafter, the portion formed of a material exhibiting a lowhydrofluoric acid resistance is covered by using the photosensitivehydrofluoric acid etching resist material according to this embodiment.As for the examples of the portion to be covered in this manner, theyinclude the light source 116 and the optical waveguide structure 115(including the beam-like structure 111, the beam-condensing structure119 and the light emitting end 117). On the other hand, the movableportions of the element structure such as the tandem gear type drivingmechanism 112, the stabilizing spring structure 113, a bellows-likespring structure 114 and a coupling structure 118 coupling the beam-likestructure with the driving mechanism are kept exposed. Incidentally, theSiO₂ layer 2102 located immediately below the beam-like structure 111 iskept exposed. Thereafter, the hydrofluoric acid etching is performed soas to remove the SiO₂ layer 2102 as a sacrificial layer and the movableportion of the element structure is made free from the Si substrate2101. Details of the method are almost the same as the opticalpatterning etching method which was already explained above.

By covering with the photosensitive hydrofluoric acid etching resistmaterial of this embodiment in this manner, it is possible to remove thesacrificial layer to make the element structure movable withoutdestroying the optical waveguide structure 115 which is composed of amaterial of low hydrofluoric resistance.

In this case, if the hydrofluoric acid etching material is notphotosensitive and hence it is impossible to perform the hydrofluoricacid etching after the formation of the optical waveguide structure 115,the optical waveguide structure 115 is required to be formed, after thehydrofluoric acid etching step, on the SOI substrate 121 having themovable portion and being complicated in structure. This leads to thecomplication of the manufacturing steps of semiconductor devices.

Further, if the concentration of hydrofluoric acid is low on theoccasion of hydrofluoric acid etching, the step of hydrofluoric acidetching would be prolonged.

The photosensitive hydrofluoric acid etching resist material accordingto this embodiment may not necessarily be required to be removed afterfinishing the manufacture of a semiconductor device. This manufacturingmethod of semiconductor devices will be explained as follows. Namely,this manufacturing method comprises: forming a portion formed of amaterial exhibiting high hydrofluoric acid resistance on thesemiconductor substrate; forming a portion formed of a materialexhibiting low hydrofluoric acid resistance on the portion formed of amaterial exhibiting high hydrofluoric acid resistance; covering theportion formed of a material exhibiting low hydrofluoric acid resistanceby using the photosensitive hydrofluoric acid etching resist material ofthis embodiment; and etching the portion formed of a material exhibitinghigh hydrofluoric acid resistance by using a hydrofluoric acid solution.

Next, an LED representing one example of the semiconductor deviceaccording to one embodiment of the present invention will be explainedin detail. First of all, one example of the LED will be explained withreference to FIG. 16.

The LED shown in FIG. 16 comprises: a compound semiconductor substrate125 formed of n-GaP and provided on the bottom surface thereof with afirst electrode 129; a light emitting layer 126 of hetero structurewhich is formed on the substrate, this light emitting layer 126comprising a clad layer 2601 formed of n-InAlP, an active layer 2602formed of InGaAlP and a clad layer 2603 formed of p-InAlP; a currentdiffusion layer 127 formed on the light emitting layer 126 and formed ofp-GaP; a second electrode 128 formed on the current diffusion layer 127and formed of Au; and a wiring electrode pattern 130.

In the case of this LED, the first electrode 129, the second electrode128 and the wiring electrode pattern 130 are formed of a materialexhibiting a low hydrofluoric acid resistance, and the hydrofluoric acidetching is performed in the step of applying a frost treatment on thesurface of the current diffusion layer 127.

Incidentally, this frost treatment means a treatment to form a ruggedsurface on the surface of compound semiconductor constituting an LEDchip by applying hydrofluoric acid etching to the surface of compoundsemiconductor. By increasing the surface area of compound semiconductorconstituting an LED chip, it is possible to enhance the light extractingefficiency.

Next, the method of manufacturing the LED will be explained withreference to FIG. 16 showing the LED.

First of all, by known techniques such as the metal organic chemicalvapor deposition (MOCVD) method or molecular beam epitaxy (MBE) method,the clad layer 2601, the active layer 2602, the clad layer 2603 and thecurrent diffusion layer 127 are successively formed on the compoundsemiconductor substrate 125.

Then, by the conventional lithography technique, sputtering techniqueand electrolytic plating technique, the first electrode 129, the secondelectrode 128 and the wiring electrode pattern 130 are formed.

Subsequently, by spin-coating method, the photosensitive hydrofluoricacid etching resist material of this embodiment is coated on the currentdiffusion layer 127. Thereafter, by using a mask having a pattern formedtherein so as to cover the second electrode 128 and the wiring electrodepattern 130, the substrate is subjected to a series of steps includingexposure, PEB, development, hydrofluoric acid etching and the removal ofprotecting film. The details of these steps may be the same as alreadyexplained with reference to the optical pattern etching method. In thiscase, the step of hydrofluoric acid etching corresponds to so-calledfrost treatment.

Subsequently, the substrate is subjected to dicing treatment topartition it into a plurality of chips, and then, wiring is connectedwith the first electrode 129 and the second electrode 128 to accomplishthe manufacture of the LED as shown FIG. 16.

In this case, if the hydrofluoric acid etching resist material is notphotosensitive and hence it is impossible to perform the hydrofluoricacid etching after the formation of the first electrode 129, the secondelectrode 128 and the wiring electrode pattern 130, these components arerequired to be formed on the rugged surface after the step of frosttreatment, thus resulting in the complication of the manufacturing stepsof the LED. Otherwise, it would be difficult to perform the frosttreatment on the surfaces of the compound semiconductor on which thefirst electrode 129, the second electrode 128 and the wiring electrodepattern 130 are formed, thereby making it impossible to improve thelight extracting efficiency.

Further, if the concentration of hydrofluoric acid is low on theoccasion of hydrofluoric acid etching, the step of hydrofluoric acidetching would be prolonged.

Incidentally, it is of course possible to perform the frost treatmentalso on the surface provided with the first electrode 129 of thecompound semiconductor substrate 125 by the same method as describedabove.

As for the materials constituting the LED shown in FIG. 16, it is alsopossible to employ the following materials other than those shown inFIG. 16. Namely, as for the compound semiconductor substrate 125, it ispossible to employ n-GaAs, n-GaP and p-GaP. As for the current diffusionlayer 127, it is possible to employ p-InAlP and p-GaP. As for the firstelectrode 129, it is possible to employ AuGa/As and AuGe/As. As for thesecond electrode 128, it is possible to employ AuZn/Au, etc.

As explained above, it is now possible, through the employment of thephotosensitive hydrofluoric acid etching resist material according tothis embodiment, to perform the optical pattern etching method using ahydrofluoric acid solution of high concentration, thereby making itpossible to simplify the process and shorten the time period in themanufacturing method of semiconductor devices.

As far as this manufacturing method is concerned, the step of removingthe photosensitive hydrofluoric acid etching resist material is nolonger required. Since the resin of this embodiment is excellent intransmittance in a wide range of wavelength, the manufacturing method ofsemiconductor devices using this resin would be especially useful in themanufacture of photochemical semiconductor devices such as an opticalscanning apparatus, an LED, etc.

Although some examples will be explained below, the present inventionwould not be limited to these examples but can be variously modified aslong as the inventive concept of the present invention can be retained.

The photosensitive hydrofluoric acid etching resist material of thisembodiment was examined in various tests including (Test A) Hydrofluoricacid resistance test; (Test B) Process test; (Test C) Test on the mainchain, alicyclic group and substituent group; (Test D) Compositiondependency test; and (Test E) Optical scanning apparatus test.

(Test A) Hydrofluoric Acid Resistance Test:

The hydrofluoric acid corrosion/decomposition resistance of the resinitself was investigated.

In Example A1, the resin represented by the formula (PS2) (m:n=50:50)was immersed in an aqueous solution containing hydrofluoric acid at aconcentration shown in Table 7. In this case, the hydrofluoric acid wassuitably diluted by using concentrated hydrofluoric acid of 49%concentration (Tokyo Kasei Co., Ltd.).

Incidentally, the resin represented by the formula (PS2) was synthesizedby the aforementioned synthesizing method.

In Comparative Example A1, OFPR-800 (Tokyo Ohka Co., Ltd.) was employedas a photosensitive hydrofluoric acid etching resist material fornovolac-based resin.

In Comparative Example A2, TDUR-P015 (Tokyo Ohka Co., Ltd.) was employedas a photosensitive hydrofluoric acid etching resist material forpolyvinylphenol-based resin.

In Comparative Example A3, polymethylmethacrylate (PMMA) (Mw=15000, typeNo. 424, Scientific Polymer Product Inc.) was employed.

TABLE 7 Concentration of hydrofluoric acid 49% 45% 40% 35% 30% 25% 20%Example A1 ◯ ◯ ◯ ◯ ◯ ◯ ◯ Comp. Ex. 1 X X X X X ◯ ◯ Comp. Ex. 2 X X X X X◯ ◯ Comp. Ex. 3 X X X X X X ◯

It will be recognized from the results shown in Table 7 that while thehydrofluoric acid corrosion/decomposition resistance of Example A1 wasretained even if the concentration of hydrofluoric acid was 30% or more,the hydrofluoric acid corrosion/decomposition resistance of ComparativeExamples A1 to A3 was retained only when the concentration ofhydrofluoric acid was 25% or less. Since the photosensitive hydrofluoricacid etching resist material of this embodiment is excellent inhydrofluoric acid corrosion/decomposition resistance, the time requiredfor the immersion thereof in hydrofluoric acid can be shortened.

On the other hand, when the materials of Comparative Examples A1 to A3were respectively coated on the substrate and the coated substrates wereimmersed in an aqueous solution of hydrofluoric acid of 49%concentration, the materials of Comparative Examples A1 to A3 were foundpoor in adhesion to substrate and also in hydrofluoric acid penetratingresistance, thus enabling these materials to be easily removed. Whereas,as described hereinafter in the Tests B to D, the photosensitivehydrofluoric acid etching resist material of this embodiment wasexcellent in hydrofluoric acid penetrating resistance, thus making itpossible to employ as a photosensitive hydrofluoric acid etching resistmaterial.

It will be recognized from these facts that as compared with theconventional etching resist materials, the photosensitive hydrofluoricacid etching resist material of this embodiment is more excellent inhydrofluoric acid resistance.

The same experiments as performed on the photosensitive hydrofluoricacid etching resist material were also applied to the substrate.

As a result, it was found that while it was possible, in the case ofetching a GaP substrate, to perform the etching using hydrofluoric acidat such a low concentration of about 20%, it was required however, inthe case of etching a quartz glass substrate (QJ Asashi Glass Co.,Ltd.), to employ hydrofluoric acid of not less than 30% in concentrationif it was desired to prevent the prolongation of the immersion step.Therefore, if it is desired to employ a quartz glass substrate, theemployment of the photosensitive hydrofluoric acid etching resistmaterial of this embodiment is especially preferable.

(Test B) Process Test:

The process test of the photo lithography was performed.

The resin represented by the formula (PS2), and 1 wt % (based on theresin) of (4,7-dihydroxy-1-naphthalenyl) dimethylsulfoniumtrifluoromethane sulfonic acid (NDS-165; Midori Kagaku Co., Ltd.) weremixed together and dissolved in propylene glycol mono methyl etheracetate (PGMEA) (Wako Junyaku Co., Ltd.) employed as a solvent, therebypreparing varnish containing the resin at a concentration of 20 wt %.

By setting the rotational speed to 1500 rpm in spin coating, thephotosensitive hydrofluoric acid etching resist material was coated oneach of the substrates shown in Table 8. Thereafter, the layer coatedwas prebaked for 90 seconds at a temperature of 120° C. to vaporize thesolvent. As a result, a layer of the photosensitive hydrofluoric acidetching resist material having a thickness of 0.86 μm was obtained.

Then, by using a mask provided with a line & space pattern, the layerwas exposed to the irradiation of g-ray of mercury lamp at an exposuredosage of 400 mJ/cm² by using a parallel exposure apparatus (Canon Co.,Ltd.; type: PLA-501). The irradiation was performed by directlysuperimposing the mask on the substrate, thereby achieving amagnification exposure of 1:1.

Then, the substrate was heated over a hot plate for 90 seconds at atemperature of 110° C. (PEB temperature).

Then, by using an alkaline developing solution composed of a solutionwhich was obtained by diluting an aqueous solution of tetramethylammonium hydroxide (2.38% TMAH) (Tama Kagaku Co., Ltd.; type No. AD-10)with pure water as shown in Table 8, the development of the coated layerwas performed for 60 seconds to form a pattern, the surface of which wasthen observed by using a super depth shape measuring microscope (KeyenceCo., Ltd.; type No. VK-8500), thereby confirming the resolution of thepattern.

Subsequently, the substrate was immersed in an aqueous solution ofhydrofluoric acid of 49% concentration (Tokyo Kasei Co., Ltd.) for 10minutes.

Then, by using a parallel exposure apparatus (PLA-501), the substratewas exposed to g-line of mercury lamp at an exposure dosage of 400mJ/cm² and then the substrate was heated over a hot plate for 90 secondsat a temperature of 110° C. Finally, the substrate was immersed inalkaline developing solution (AD-10 (2.38% TMAH); Tama Kagaku Co., Ltd.)for 60 seconds to dissolve and remove all of the photosensitivehydrofluoric acid etching resist material. The surface of the substratethus obtained was then observed by using a super depth shape measuringmicroscope (Keyence Co., Ltd.; type No. VK-8500), thereby confirming theresolution of the pattern.

The resolution of the photosensitive hydrofluoric acid etching resistmaterial subsequent to the developing step and the resolution of thesubstrate after finishing all of the steps are shown in the followingTable 8.

TABLE 8 Degree of Resolution of diluting photosensitive Resolution ofalkaline composition substrate developing after developing after entireSubstrate solution step (μmL/S) steps (μmL/S) Ex. B3 GaP 20 times 7 8Ex. B4 Quartz 20 times 7 8

It will be recognized from the results shown in Table 8 that the photolithography method using the photosensitive hydrofluoric acid etchingresist material of this embodiment was capable of obtaining a patternhaving a resolution of about 8 μmL/S through the exposure using theg-line of mercury lamp, thereby making it possible to provide excellentresolution.

It will be also recognized from the results shown in Table 8 that thedegree of dilution of the alkaline developing solution should preferablybe set to 20 times.

(Test C) Test on the Main Chain, Alicyclic Group and Substituent Group:

EXAMPLE C1

A test was performed in the same manner as that of Example B3 exceptthat the resin represented by the formula (PS2) (m:n=50:50) was employedand the PEB temperature was changed to 120° C. was performed.

EXAMPLE C2

A test was performed in the same manner as that of Example C1 exceptthat the resin represented by the formula (PS3) (m:n=50:50) wasemployed.

EXAMPLE C3

A test was performed in the same manner as that of Example C1 exceptthat the resin represented by the formula (PS4) (m:n=40:60) wasemployed.

EXAMPLE C4

A test was performed in the same manner as that of Example C1 exceptthat the resin represented by the formula (PS5) (m:n=40:60) wasemployed.

EXAMPLE C5

A test was performed in the same manner as that of Example C1 exceptthat the resin represented by the formula (PS6) (m:n=50:50) wasemployed.

EXAMPLE C6

A test was performed in the same manner as that of Example C1 exceptthat the resin represented by the formula (PS7) (m:n=60:40) wasemployed.

The results of these test thus obtained are shown in Table 9.

Results of test Resolution of Concentrated Resin substrate afterhydrofluoric Number m:n entire steps acid (49%) Main chain Alicyclic ofOH (mol) (μmL/S) resistance Ex. C1 Acrylate Adamantane 1 50:50 7.0 60min. or more Ex. C2 Methacrylate Adamantane 1 50:50 20.0 60 min. or moreEx. C3 Acrylate Adamantane 2 40:60 5.0 10 min. Ex. C4 MethacrylateCyclohexane 1 40:60 3.0 30 min. Ex. C5 Acrylate Isobornene 1 50:50 8.060 min. or more Ex. C6 Acrylate Tricyclodecane 1 60:40 12.0 60 min. ormore

The resin of Example C1 was more excellent in resolution andhydrofluoric acid resistance as compared with the resin of Example C2.Therefore, it will be recognized that the main chain should morepreferably be constituted by acrylate rather than methacrylate.

The resin of Example C1 was more excellent in resolution andhydrofluoric acid resistance as compared with the resin of Example C3.Therefore, it will be recognized that the number of hydroxyl groupshould most preferably be only one.

The resin of Example C4 was more excellent in resolution, thoughhydrofluoric acid resistance was somewhat inferior, as compared with theresins of Example C1, C5 and C6. Therefore, it will be recognized thatthe resin where the alicyclic group was constituted by cyclohexane wouldbe more preferable for use in the application where a higher resolutionis desired.

Incidentally, although a desirable magnitude of resolution andhydrofluoric acid resistance may differ depending on the application, itis assumed practically sufficient if the resolution is several tens ofμmL/s, and the hydrofluoric acid resistance is about 5 minutes.

It was confirmed that even if a resin wherein norbornene was introducedtherein as an alicyclic group was employed, it was possible to obtainalmost the same results as described above. Further, although a resinwherein cyclooctane was introduced therein was found somewhat inferiorin hydrofluoric acid resistance, the resolution thereof was excellent sothat the resin was found quite satisfactory in practical use.

(Test D) Composition Dependency Test:

By changing the composition ratio of m:n of the resin represented by theformula (PS2), tests were performed in the same manner as explained inTest B.

The results of these test thus obtained are shown in Table 10.

TABLE 10 Resolution Concentrated of substrate hydrofluoric M:n afterentire acid (49%) (mol) steps (μmL/S) resistance Ex. D3 30:70 50 60 min.or more Ex. D4 40:60 12.0 60 min. or more Ex. D5 50:50 7.0 60 min. ormore Ex. D6 60:40 4.0 30 min. Ex. D7 70:30 2.0 10 min. Ex. D8 80:20 2.0 1 min. or less Ex. D9 90:10 2.0  1 min. or less

When the ratio between m:n was confined within the range of 30:70 to70:30, the resolution and hydrofluoric acid resistance of the resin wereboth preferably increased.

Incidentally, the aforementioned composition ratio m:n shown in Table 10is expressed by the ratio of monomers charged on the occasion of thepolymerization of resin. The method of polymerizing the resin of thisembodiment was a synthesizing method which was designed to obtain arelatively high yield. The difference between the ratio of monomerscharged on the occasion of the polymerization of resin and the ratio ofsegments m:n after the polymerization of resin was very limited, fallingwithin an allowable error.

However, if a method enabling a shortened reaction time is employed, thereaction would be taken place from the monomers which are more reactive,thereby exhibiting a tendency of decreasing the generation of bulkysegment. As a result, there may be occurred a difference between theratio of monomers and the ratio of segments, thus necessitating suitableadjustment of these ratios. When non-uniformity of these ratiosdepending on the selection of synthesizing methods is taken intoaccount, a preferable range of composition in terms of the ratio ofmonomers (m:n) is assumed to be confined within the range of 25:75 to75:25.

(Test E) Optical Scanning Apparatus Test:

By using the photosensitive hydrofluoric acid etching resist material ofthis embodiment, the optical scanning apparatus shown in FIGS. 14A, 14Band 15 was manufactured. Incidentally, in this optical scanningapparatus thus manufactured, the width and length of the beam located atthe center of the element constituting a main point of the scanning were10 μm and 1300 μm, respectively.

The method of manufacturing the optical scanning apparatus shown inFIGS. 14A, 14B and 15 will be explained with reference to FIGS. 17A to17I.

FIGS. 17A to 17I are schematic partial sectional views each illustratingmethod of manufacturing the optical scanning apparatus.

As shown in FIG. 17A, the substrate to be employed in the elementmanufacturing process is formed of an SOI substrate 121, which can bemanufactured by connecting a Si active layer 2103 via an SiO₂ layer 2102onto a Si substrate 2101. In this Test E, the SOI substrate 121(available from Toshiba Ceramics Co., Ltd.) was constructed such thatthe Si substrate 2101 was formed of non-doped silicon, the SiO₂ layer2102 was formed to have a thickness of 2 μm, and the Si active layer2103 was formed of n-type high-doped silicon.

As shown in FIG. 17B, a resist layer 122 is coated on the SOI substrate121. Thereafter, various portions corresponding respectively to abeam-like structure 111 constituting a component element of the opticalscanning apparatus, a movable element structure comprising a couplingstructure 118 connecting the beam-like structure with a drivingstructure and a tandem gear type driving mechanism 112, and an opticalwave guide structure 115 are exposed to light.

As shown in FIG. 17C, by chemical vapor deposition (CVD), a metallicmembrane layer 123 is formed on the exposed portions. Thereafter, theresist layer 122 is removed to obtain a pattern of the metallic thinfilm 123 which corresponds to the element structure.

As shown in FIG. 17D, a raw material to be formed into the optical waveguide structure 115 is coated on the SOI substrate 121 provided with thepattern of the metallic thin film 123.

As shown in FIG. 17E, a resist layer 122 is coated on a layer of rawmaterial to be turned into the optical wave guide structure 115.

As shown in FIG. 17F, the resultant substrate is subjected to exposureand development so as to cover the top surface of the portion to beturned into the optical wave guide structure 115.

As shown in FIG. 17G, by reactive ion etching (RIE), portions other thanthe portion to be turned into the optical wave guide structure 115 arecut out. On the occasion, in the surface on which the metallic thin film123 is not formed, the Si active layer 2103 is also cut out.

As shown in FIG. 17H, the resist layer 122 is removed and then by usingthe photosensitive hydrofluoric acid etching resist material of thisembodiment, the optical wave guide structure 115 is protected.

As shown in FIG. 17I, by hydrofluoric acid etching, the SiO₂ layer 2102to be used as a sacrificial layer is removed. As a result of this step,the element structure is made movable. Incidentally, the specificconditions on this occasion are the same as those of Test B.

As explained above, in the case of the optical scanning apparatusmanufactured in this Test E, since the etching of the sacrificial layercan be performed after the manufacture of the optical wave guidestructure 115, the manufacturing method of the apparatus can besimplified and the time required for the manufacture thereof can beshortened.

According to this embodiment, there are provided a photosensitivehydrofluoric acid etching resist material which is excellent inhydrofluoric acid resistance, an optical pattern etching method whichenables concentrated hydrofluoric acid etching, and a method ofmanufacturing a semiconductor device which makes it possible to simplifythe manufacturing process and to shorten the time required for themanufacture.

While various embodiments of the present invention have been explainedabove, it is evident that the present invention is not restricted tothese embodiments but can be modified variously without departing theessential characteristics thereof described in the appended claims.Further, in actual use, the present invention can be modified variouslywithout departing the essential characteristics thereof. Furthermore, aplurality of constituent elements disclosed in the foregoing embodimentsmay be optionally combined to form various embodiments of the presentinvention.

Additional advantages and modifications will readily occur to thoseskilled in the art. Therefore, the invention in its broader aspects isnot limited to the specific details and representative embodiments shownand described herein. Accordingly, various modifications may be madewithout departing from the spirit or scope of the general inventiveconcept as defined by the appended claims and their equivalents.

1. A semiconductor device having a roughened side surface comprising asemiconductor substrate having a roughened side surface; a firstelectrode; a light emitting layer formed above the semiconductorsubstrate having the roughened side surface; and a second electrode; thesemiconductor device being manufactured by a method comprising: forminga protective film on a part of surfaces of the semiconductor device, thesemiconductor device having an side exposed surface, the protective filmcomprising an acid etching resistance material having a repeating unitrepresented by the following general formula (1):

wherein in the general formula (1), R¹ is a hydrogen atom or methylgroup; R³ is a cyclic group selected from an alicyclic group and anaromatic group; R⁴ is a polar group; and R² is a group represented bythe following general formula (2):

wherein in the general formula (2), R⁵ is a hydrogen atom or methylgroup; immersing the semiconductor device into an acid solution, therebyetching the exposed side surface of the semiconductor device to form theroughened side surface; and removing the protective film.
 2. Thesemiconductor device according to claim 1, wherein the protective filmcovers at least the first electrode and the second electrode.
 3. Thesemiconductor device according to claim 2, wherein the first electrodeis provided on a surface of the semiconductor substrate.
 4. Thesemiconductor device according to claim 3, wherein the second electrodeis provided above the light emitting layer.
 5. The semiconductor deviceaccording to claim 1, wherein the light emitting layer is formed above apart of surfaces of the semiconductor substrate.
 6. The semiconductordevice according to claim 1, wherein the protective film comprises alower protective film and an upper protective film on the lowerprotective film.
 7. The semiconductor device according to claim 6,wherein the upper protective film is formed of a novolac resin.
 8. Thesemiconductor device according to claim 1, wherein the semiconductordevice is a light emitting element.
 9. The semiconductor deviceaccording to claim 1, wherein R³ in the general formula (1) is analicyclic group selected from adamantane, norbornane, and cyclohexanering.
 10. The semiconductor device according to claim 1, wherein R³ inthe general formula (1) is an aromatic group selected from benzene andnaphthalene ring.
 11. The semiconductor device according to claim 1,wherein R⁴ in the general formula (1) is —OH, —COOH, and =O.
 12. Thesemiconductor device according to claim 1, wherein the acid etchingresistance material further comprises a repeating unit represented bythe following general formula (1′):

wherein in the general formula (1′), R¹ is a hydrogen atom or methylgroup; R^(3′) is a cyclic group; R⁴ is a polar group.
 13. Thesemiconductor device according to claim 12, wherein R^(3′) in thegeneral formula (1′) is an alicyclic group.
 14. The semiconductor deviceaccording to claim 13, wherein the alicyclic group is selected fromadamantane, norbornane, and cyclohexane ring.
 15. A semiconductor devicehaving a roughened side surface comprising a semiconductor substratehaving a roughened side surface; a first electrode; a light emittinglayer formed above the semiconductor substrate having the roughened sidesurface; and a second electrode; the semiconductor device beingmanufactured by a method comprising: forming a lower protective filmabove a part of surfaces of the semiconductor device using a firstsolution containing a first solvent and an acid etching resistancematerial, the semiconductor device having an exposed side surface, thelower protective film being insoluble to a second solvent, the acidetching resistance material having a repeating unit represented by thefollowing general formula (1):

wherein in the general formula (1), R¹ is a hydrogen atom or methylgroup; R³ is a cyclic group selected from an alicyclic group and anaromatic group; R⁴ is a polar group; and R² is a group represented bythe following general formula (2):

wherein in the general formula (2), R⁵ is a hydrogen atom or methylgroup; forming an upper protective film using a second solutioncontaining the second solvent on the lower protective film, therebyobtaining a protective film formed of a laminated structure comprisingthe lower protective film and the upper protective film; immersing thesemiconductor device into an acid solution, thereby etching the exposedside surface of the semiconductor device to form the roughened sidesurface; and removing the protective film.
 16. The semiconductor deviceaccording to claim 15, wherein the second solvent comprisespropyleneglycol monomethyl ether acetate.
 17. The semiconductor deviceaccording to claim 15, wherein the upper protective film is formed of anovolac resin.
 18. The semiconductor device according to claim 15,wherein R³ in the general formula (1) is an alicyclic group selectedfrom adamantane, norbornane, and cyclohexane ring.
 19. The semiconductordevice according to claim 15, wherein the acid etching resistancematerial further comprises a repeating unit represented by the followinggeneral formula (1′)

wherein in the general formula (1′), R¹ is a hydrogen atom or methylgroup; R^(3′) is a cyclic group; R⁴ is a polar group.